She was a member of the Mutant Underground until she defected to join Hellfire Club. Although, her sentimental attachments to the Underground remain, Sage left due to the Hellfire Club producing results in their fight for freedom that the Underground hasn't stopping Trask Industries and the Hound program.
Little is known of Sage's early life, though she was once a homeless refugee until she met Polaris, who brought her to the station and helped Sage get clean. She later became a resourceful member of the Mutant Underground by not only monitoring all activity of law enforcement and mutants alike, but by determining which mutants get to stay in their care and which had to leave.
In eXposed, Sage speaks to the new arrival at the Mutant Underground Headquarters, Blink. She learns that Blink's birth name is Clarice. Sage then asks her if she should contact anyone, perhaps family, to which Clarice says it is complicated. Sage then informs her that she would stay with them at the headquarters until they figure out where they will relocate her
In rX, after the new arrival, Clarice, loses control of her abilities and nearly destroys the Headquarters, Sage joins Sonya and the others in reestablishing order.
In eXodus, Sage sits alongside Shatter and Sonya as John and Marcos discussed their next course of actions in rescuing Lorna and Reed Strucker from Sentinel Services' custody. Marcos wants to act immediately, but John wants to wait, and assess the situation from a more level-headed perspective given that they would have to face 20 ft walls with guards armed with guns. Sonya interjects, agreeing with Marcos in regards to first training Clarice who had almost destroyed the station due to her unstable abilities, and then using her to break Lorna out. Outnumbered and under pressure, John caves, deciding then and there to save Lorna the first opportunity they get.
The next day, in the monitoring cell, Sage grows concerned after learning that Thunderbird and Eclipse are under attack by the "local mutant welcoming group" after they retrieved the Struckers, who had left the station one day prior despite being advised against it. Fortunately, Sonya devises a plan to save them.
In eXit strategy, two years ago, the Underground infiltrates a mutant relocation center somewhere in Georgia. Sage, Eclipse and two other members, Randall and Elsa, move forward towards the second fence while Thunderbird and Pulse stay behind to wait for their signal. Unfortunately, the plan goes awry as gunshots ring out in the night. Sage and Eclipse make it back to them alive and well, however, Randall and Elsa, weren't as fortunate. The facility's defense system of automated guns and infrared trackers are far more advanced than they had expected. With his ability to disrupt systematical electronics, Pulse volunteers to shut down their system to the automated weapons in order to buy the rest of them some time to escape. However, after successfully doing so, he s shot down and supposedly killed.
Present day, Sage joins the rest of the Underground as John and Marcos inform them that Lorna and Reed Strucker are being held in a cell at the Sentinel Services regional Headquarters. They would soon be relocated to an ultra secure facility, which the Underground doesn't have much insight on beyond the fact that the people who go there, don't come back, thus forcing their hand in attacking the Sentinel Services head on. Unfortunately, many members are reluctant in volunteering to join the break out mission to save Lorna and Reed, including Sage, who reminds John and Marcos that they lost six people the last time they went up against the Sentinel Services, which was merely a relocation center with a fence and a few guard towers. This time around it was a prison they were attempting to infiltrate, whose systems had improved. Extrapolating from other attacks, the Underground had an 86.5% chance of failure, Sage determines. But as Marcos explains, if they did nothing, then there's a 100% chance of never seeing Reed or Lorna again. Furthermore, Sage owes Lorna, who found her in a gutter, and cleaned her up. Despite the history Sage shares with Lorna, she decides against joining in on the mission to rescue her given the likelihood of the plan's failure.
In boXed in, after John returns from successfully saving Lorna and Reed from the convoy, she informs him that Sentinel Services is now striking back. They had started raiding every known safe house and pursuing all known and suspected sympathizers in retaliation, without warrants, she adds. Sentinel Services is undoubtedly out for blood. Between a station full of refugees, and all the heat being brought down on them, they have their hands full. While Sage is putting her efforts into manning the scanner and keeping their people off the grid, John instructs her to inform him if anything important shows up.
After a while, it seemed as if Sentinel Services had stopped making moves over the police radios, leaving Sage to conclude that they had given up on the search. So she informs John of the sudden radio silence. Until a few minutes ago, the scanners were going wild with activity in regard to the manhunt, but it suddenly stopped. Over the radio, they can hear a traffic stop being called in, before that, a drunk and disorderly by the freeway. Reed interjects, explaining to them that the manhunt was still in full effect. He offers to help as he used to work similar manhunts, and therefore knows the protocol. Dispatch calls in all units for a petty theft. So Reed asks for a map, marking on it the last three calls; a burglary in Stratford, lewd conduct at a bar in Hapeville, and a 586 in Glen Haven. They sent multiple units to all of three places, which means that they know the Underground is listening. So they have resorted to speaking in code. While Sentinel Services searched for Eclipse and Polaris, Atlanta PD is tightening a net, working a grid, looking for the Underground.
As they continued to listen to the scanner, John contemplats evacuating the station in preparation for the cop's arrival. Sage however advises him against such actions given that any identifiable mutants leaving the Underground will be apprehended before they are out of city limits. Since they are looking for fugitives, Reed suggests that he go out there to draw them away from Headquarters by making it seems as if they are in a different direction. Reed explains that Sentinel Services made an educated guess about the direction they went in, so if they were to see Reed anywhere in the opposite direction, they would assume that he is going to 85 South, toward Alabama, and they would redirect the search that way. But as Sage points out, if he gets caught, they will arrest and interrogate him, thus compromising the station. Maybe there is a way we could avoid that, John states, as he looks over to Fade.
After coming up with a plan to redirect the manhunt, Sage and John monitor the scanners, waiting for the call to come in for Reed, who is to let himself be seen on surveillance cameras to lure Sentinel Services away. Before long, the call comes in. They hear over the scanners that he had indeed been made and that police are moving in on him. She and John watched as law enforcement redirect their search south. Sage texts Reed to alert him that he had been made, and that he needs to get out of the immediate area. Reed is then picked up by Fade, who cloaks his car and drive off, thus a successfully executed plan.
In got your siX, Sage John, Marcos Reed, Shatter, Lorna, and Sonya gathered around a table, where they look over the schematics for the Baton Rouge Federal Building, and try to formulate a plan in their attack on Sentinel Services. Reed tells them of his knowledge of the building. Some of his cases had been transferred to Baton Rouge. There is a judge James Kresge that works there. He dealt with most of Reed's cases. Shatter questions how many people Reed prosecuted that disappeared through the building. Reed says it was rare and that all they told him was that some of his cases were being prosecuted under a special federal program. Marcos is now concerned with getting past the wall to the files, which he plans on Clarice getting them to. John takes that opportunity to reveal to everyone that Clarice left. Having eavesdropped on their entire discussion, Andy volunteers to get them through the wall, as he can do it faster than Marcos, who claims he can cut through it.
The next day, in the monitoring cell, Sage and Shatter learn from John that Headquarters in Alpharetta was hit. They manage to get about half of their people out, who are on their way to the station. However, as Sage explains, given the current influx of refugees, they are already 78% over capacity. John apologizes for the inconvenience, but they don't have any other choice.
In eXtreme measures, Sage, Marcos, Lorna, Sonya, and Reed convene in the monitoring cell, where John reveals that after talking to another station, he had learned that Sentinel Services is ramping up surveillance across the board, meaning things are going to get worse before they get better. Unfortunately, they are running out of supplies with the influx of refugees. So, Marcos volunteers to take a drive up to Marietta, where he supposedly heard that they had supplies to offer. John turns his attention to the hard drives from Baton Rouge, which Sage and Reed are working on. They are encrypted, but that likely means that there is something worth hiding on them. If they don't find out how Sentinel Services is turning mutants against each other, all their work will have been for nothing. Lastly, John announces that he will be leaving soon to track down Clarice. She knows the station's location, which can compromise the entire organization if she is apprehended.
While they attempt to crack the hard drives from Baton Rouge, Reed notes that the first drive is solely police files on mutants. However, on Sage's file, the encryption runs much deeper. Reed suggests that maybe they are dealing with a shopping list. It seems as if Sentinel Services is picking specific mutants to participate in whatever program they are working with, based on their powers. They aren't even pretending as if it is legal.
Sage and Reed continue their efforts on the encrypted drives. As Reed takes everything there is to take from the files, Sage works on the second drive, calculating relationships with asymmetrical algorithmic keys. Reed inquires about her secondary duty of evaluating the mutants that are brought into the station. With so many mutants running from the law, Reed wonders how she determines whether or not to allow someone to stay or leave. There are certain things that they didn't forgive, such as murder, rape, and victimizing other mutants. Other than that, she only asks that everyone tell the truth because the station is built on trust. Should they fail to adhere, then they are forced to leave.
The next day, after cracking most of the hard drives' security, Sage informs John that it mostly contained information in regard to mutants who were sent into Sentinel Services' program, Pulse was one of those mutants. He was one of the first. Unfortunately, all they had were the courthouse records of who was selected. Sage knows nothing of a location for the program. However, with it being run by the Sentinel Services, there has to be a record given that it was a government program, though Sage isn't certain that it is a government program. She explains that it is actually run by a private military contractor, Trask Industries, which Reed is familiar with since his father worked there for 35 years. However, it supposedly closed down in 2006. John questioned if Reed's father has any involvement with the program, though Reed is unsure.
In threat of eXtinction, Sage types from the monitoring cell as John instructs Shatter to speak with the station in Gainsville to make sure they're prepared for more refugees.
Upon John, Marcos and Clarice's return from Perry, where they had picked up survivors from the fallen station, Sage learns that they were attacked by one of Sentinel Services' mutant assets from the program. The yet to be named woman attacker is locked in a cell. They describe her as being a cross between a spy and a suicide bomber. She had a beacon in her back that she could've activated once they arrived at the station, which would've compromised the entire organization by leading Sentinel Services to them. She had weapons as well. With Sentinel Services planting them out into the world, Sage suggests that they stop taking in refugees for the time being. However, as John refuses to turn their back on desperate people just because one of them might be dangerous.
Sage later watches as Lorna and Sonya attempt to get answers from the prisoner by manipulating her memories since she had refused to talk. Although, Sonya agreed to give it a try, she isn't convinced that it will work. Sonya exhales her pink smoke, but the prisoner is too fast, avoiding the smoke. Sonya explains that she isn't equipped to hit moving targets. Furthermore, had the prisoner breathed in the smoke, her metabolism is likely too fast for for any information of use to be gathered from her memories. This forces Lorna to resort to more violent means of interrogation, as she threatens the prisoner at knife point. Fortunately, before things can get out of hand, Marcos arrives to bring an end to Lorna's savage style of interrogation.
After looking through the hard drives from Baton Rouge, Sage returned with the prisoner's identity. Her name is Chloe Tan. She used to live in a trailer park outside of Jasper. Her kid got sick, but the pediatrician wouldn't treat mutants, so Chloe destroyed the doctor's office, and was subsequently apprehended by Sentinel services. Caitlin had drugged Chloe in order to move her to a table for proper treatment. As she wakes up, Caitlin attempts to speak to her. They know she was arrested by the Sentinel Services, but they need to know what happened to her while she was in their custody. Chloe attempts to communicate, but Caitlin determines that she can't speak, and she has not the slightest clue whether it is mental or physical. Caitlin then suggests that they use one of the latest refugees to come to the station, a telepathic girl named Esme, to read Chloe's mind.
In outfoX, Sage, John, Clarice, Marcos, Lorna, Sonya, and Esme gather around to discuss how best to infiltrate Trask Industries in order to recuse the apprehended mutants, which includes Esme's family. From what Esme was able to gather from Chloe Tan's mind, the mutants in Trask's lab are desperate. Esme describes being able to hear the screams, see the bodies, and feel the agony when they turned Chloe into a Hound. With Sage assembling a site map, Sonya wonders if Esme was able to gain any information on the lab's security while in Chloe's mind. Unfortunately, she wasn't. However, this matters little to Esme who is determined to break in and save her family. Marcos and Lorna are just as determined as Esme to infiltrate the lab, but going into the facility without a full understanding of the building would only result in their deaths, so they choose to hold off.
Sage has been doing surveillance of the Trask lab. What she discovers is that it is located in the middle of nowhere. And while there is no information to be gathered on the location, there is a nearby bar that Sage determines is popular with Trask employees. Sonya volunteers to go into the bar and pull information from a guard or operations person. Marcos offers to join her in case the mission turns violent, however, Lorna reasons that they have better chances of obtaining the information they need if two girls went in, rather than a guy. They were right, as Lorna and Sonya manage to gain the information needed.
They all later regroup to discuss how the lab is hardened against mutant attack. They have motion and infrared sensors connected to heavy-caliber guns that are mounted all over the building. Neither Lorna nor Clarice can get them past Trask's defenses. Luckily, Sage managed to find one vulnerability. A power substation a few miles away. If they take it out, they can gain access to the lab before Trask's systems get back online. However, they don't have enough combat ready mutants to hit the station and the lab at the same time. So, they are checking with other stations to presumably see who would join them.
Sage, John, Marcos, Sonya, Clarice, Lorna and Esme call down the Struckers to ask if Reed and Caitlin are willing to allow Andy and Lauren to disengage the substation transformers, similar to how they stopped the prison convoy. While it is admittedly a lot to ask, they have no other choice as everyone else with combat powers will be assaulting the lab. Sage hacked the security cameras and the station only has a handful of guards. Clarice will portal everyone in, and from there, Sonya will guide them. They'd been through every option. Unfortunately, the plan with Andy and Lauren is the only one that can work. Both Andy and Lauren are willing to help in whatever way they can. Reed and Caitlin agree to allow the kids to take out the transformers, but only if they can monitor security. With a plan set in motion, they'll be moving out within the hour.
One hour later, they proceed with the plan.As Blink drives the Struckers to the power station, Sage gets a call from Reed, who inform her of their arrival. Sage then bypasses the fire wall, allowing Reed and Caitlin to view the security footage from the truck. She looped the feed so that security wouldn't see their team but they would notice eventually.
In 3 X 1, after discovering that Esme manipulated and betrayed the Underground in order to free family from Trask labs, Sage began doing some digging. She couldn't find much, but she knows there are three sisters. At least that they know of. Esme, Sophie and Phoebe Frost. But they often use new alias. When Sophie and Phoebe were arrested, they gave their last name as Cuckoo. Their police file says that they have a HIVE mind. Capable of limited psychic control if they can get close and the target doesn't see it coming. They're politically connected and wealthy. Sage discovers via a campaign photo that one of them (Esme), infiltrated Senator Montez's campaign last year. Clarice recognizes Montez and accuses him of being a Purifier. John worries that an alliance with the Frost Sisters will tear the station apart. However, that's already happening due to the Underground being at odds in regards to the Frost. Sage decides to separate the arguing Underground members while Clarice and John further discuss their game plan. Sage then calls John over for help as the Underground continues to fall apart.
A couple days had passed, and a lot had changed, more notably, the Struckers leaving the station as they felt they were no longer safe, especially with the Frost Sisters around. Sage interrupts John, Marcos, Lorna and Clarice's discussion to inform them that she had learned from the police scanners that something big is about to go down. Upon further analysis, she learns that Trask and Sentinel Services is about to attack the Fairburn station, where they Struckers are coincidentally residing until they can make it across the boarder. With that, Thunderbird, Eclipse, Polaris and Blink head down to save the Struckers as well as the other mutant refugees.
In eXtraction, Sage and Reed comb through his father's research, most of which was from his grad school days. It was imperative that this be done after discovering that Otto Strucker somehow found a way to suppress Reed's X-Gene. Unfortunately, they haven't found much of his work on mutants. Sage discovers that Sentinel Services is also tracking down everyone Otto Strucker's ever worked with and they're even sending agents to the Southern Worldwide Insurance company where Reed's mother works. With that in mind, Reed, Caitlin, Andy and Lauren set out to get to Ellen before Sentinel Services does.
The Struckers return to HQ, where Sage informs Reed just how lucky his timing was in getting to his mother as Sentinel Services sent another team to her house. However, she's made it out of town so far without them noticing. Trask wasn't only after Ellen though. They've sent agents to anyone whose ever met Otto. Reed tells Sage about the research that his dad worked with, Madeline Risman.
In X-roads, Sage and Shatter inform Reed and Caitlin that something went wrong at the Humanity Today Summit, which Thunderbird, Eclipse, Polaris, Blink and the Frost Sisters had sneaked into in order to prevent Dr. Campbell and Senator Montez from proceeding with their plans to move forward with the Hound program. Sage had been been monitoring the police reports and all they know for sure is that Campbell escaped.
The Underground finds themselves in a bind after getting word from Pedro that Sentinel Services had learned of their location. With that, the station is now under evacuation. As Reed, Caitlin and Fade focus on evacuating the refugees, Sage requests all hard drives and communication devices as they have to burn everything they have. She throws everything into a trash can before setting it on fire.
After destroying all hard drives and communication devices, Sage escapes with the rest of the refugees, who managed to break through the vault wall, creating an opening that allowed them to get away without being apprehended. Unfortunately, Caitlin and Reed worry that the Hounds will see them and know where they went, resulting in their capture. So Andy and Lauren volunteer to stay behind after everyone's out so that they can destroy the building in order to cover their tracks. And they do just that, completely leveling the building, with the Hounds inside.
The Underground has regrouped at the Mutant Way Station in Nashville, Tennessee. John, Marcos and Clarice arrive some time later. When they do, Sage informs them that while it was close, everyone got out. If not for Andy and Lauren, they would all be dead. Sage goes onto tell them that the station is completely gone. No one got out but Andy and Lauren. John and Marcos have an especially hard time taking this in as they've put everything into the station. Marcos asks if there's been any word from Lorna, Sage tells him that there hasn't been.
John announces that they need to start thinking about next steps. With Headquarters gone, a lot of people have nowhere to go. It's time to rebuild. It's not just about the building, but more so the network and the people in it. Although, Sage, Shatter and Fade doubt that it's even possible to start from nothing. Furthermore, Sage points out that since the Struckers arrived, half their stations have been destroyed, but Caitlin counters that the Hound program was coming one way or another. Marcos explains that the X-Men did this knowing it would take struggle and sacrifice. Lorna interrupts with Esme, telling them that there's nothing noble about struggle and that the Mutant Underground is dying. But that world that they've always talked about where they don't have to hide and live in fear, she wants to build that for them. Lorna and Esme intend to rebuild the Hellfire Club, but they need people. The people they've come for know who they are, which includes Fade, Bulk, and Sage, who apologizes to John for switching allegiance, but for her this is just about survival. Last to join them is Andy, who feels as if it's his birthright.
In eMergence, Sage and the Frost Sisters pull up to the guard's booth at the munitions warehouse, where they intend for Lorna to give birth. The Sisters use their mind control over the patrolling guard in order to gain access to the facility. Once inside, they enter the owner's office and command him to evacuate the property. However, he initially refuses, forcing Sage and the Frost Sisters to bribe him with a suitcase full of money. They instruct him to inform the others that there was a class-one toxic materials spill and that the facility needed to be evacuated. Still, the owner refuses. So, the Frost Sisters make it perfectly clear that they could force him to do what they want, but paying him off is easier. The question isn't whether this place is theirs. The question is whether he will give it to them, or they take it. With that, the facility owner agrees to their terms.
She later appears in the telepathic vision of a future, where mutants have secured a safe world for themselves, that is implanted in Lorna's head by the Frost Sisters in an effort to overcome her mental block.
In unMoored, Sage and Reeva overlook Andy from the upper deck of the training room as they test his abilities to ensure that he can successfully complete his end of an upcoming operation. Reeva informs him that the walls are made of the same materials he'll face at the target of their first operation, each stronger than the last. So she needs him to break through them. Sage monitors his activity as he breaks through each wall, one right after the other. Andy manages to break through three walls, but as he comes up on the fourth, he loses focus and run face first into the wall. Sage informs Reeva that Andy's force distribution declined drastically. With that, Reeva tells Sage to get her Fade as she has an assignment for him.
Sage and Reeva monitor Andy from above as he returns for another training session. Sage states that his kinetic energy is back to its original level and moment of inertia is climbing. Just as it seemed he would break through all the walls successfully, again, Andy begins to recall his dream of Lauren falling off the parking garage's roof, and yet again, he goes face first into the wall. Reeva looks to the Frost Sisters for answers. Esme, Sophie and Phoebe look inside Andy's mind. They discover that Lauren is the problem.
Andy now seems to be thriving during training, as he makes quick work of the boron carbide. Sage and Reeva are both impressed and pleased with his progression.
Sage presents herself as a very blunt individual. She always tells the cold and honest truth of any situation and places high value in honesty among the group. Yet, she cares about all the people in the Underground's care and does what she can to help out her friends.
Superhuman Intelligence - Sage's brain functions similar to a computer giving her higher intelligence and an inhuman level of analysis and computation, often calculating the percentage of a successful outcome to every plan. Her mind also stores data similar to a computer giving her an advanced and thorough memory.
Telepathic Immunity - The technical aspects of Sage's brain (due to being similar to a computer) make her immune to telepathy, as it's been mentioned that the Frost Sisters have had difficulty reading Sage's mind, only seeing binary code ("ones and zeroes" as stated by Esme Frost).