|“|| My name is Agent Walker, with the Federal Bureau of Investigation, and this is my associate, Agent Noto. I hope you don’t mind if we join you.
-Return to Paradise
Karen Walker was a special agent working for the Federal Bureau of Investigation. She was assigned to help the Mogadorians hunt the Garde, having been tricked into thinking the Mogadorians simply want to trade weapons for their help. She has distinctive red hair.
Walker was just out of the FBI academy when the Mogadorians first made contact. They claimed to be hunting fugitives and wanted the use the FBI's law enforcement network and free rein to move around the country in return for weapons and technology.
At some point after being recruited to work alongside the Mogadorians, Walker goes to Paradise, Ohio, to investigate the destruction of the Paradise High School. She follows Sarah Hart and tries to gain information about Number Four and Sam Goode from her and Mark James.
Sarah is later detained and interrogated by Walker, Purdy, and Noto following Four's return to Paradise. When Sarah is taken to Dulce by the Mogadorians, Walker and Noto arrive at Mark's house and ask him if he knows what Sarah was doing the night she disappeared and break the news. (Return to Paradise)
Walker shows some sadness at Sarah's disappearance and later reaveals to Mark that she did not know about the Mogadorians plan to take her. (The Fugitive)
Capturing Four and NineEdit
Walker and Purdy are able to track Four and Nine. They ambush them in an abandoned house in West Virginia and they are locked in glass cages in the back of a van. They manage to escape and the van is crashed by the Garde and flipped several times, throwing the agents around like rag dolls, severely injuring them. Four tries to get information about Sam and Sarah from Walker but she drifts in and out of consciousness. He goes outside to help Nine and when he returns, Walker has disappeared.
Walker is later seen, bandaged and slinged up at the Dulce base in New Mexico. She meets Six in her cell which she shared with Sarah and reveals her motives for aligning with the Mogs: she is only interested in invincibility using the alien weapons and iridium to be "light years ahead of any other army on Earth." She then takes Six from her cell and leads her away to battle with Setrákus Ra.
When she is spotted by Four, Eight, and Nine, they restrain her and in fear, she reveals she knows where the Garde's ship is located (although it's unknown whether she's telling the truth or just bluffing to keep the Garde from finding Six). Nine hangs her on a light fixing and Sarah is assigned to make sure she does not escape.(The Rise of Nine)
While in the Dulce base, Agent Purdy suffers a heart attack and dies. After seeing parts of Purdy's body disintegrate, Walker changes her opinion about the Mogadorians. She gathers a few rogue agents loyal to her and decides to act against them, noting that she is loyal to the American people. Walker and her rogue faction remain at Dulce for a while after its destruction in order to strip it of any valuable assets. Before they depart to surveil Ashwood Estates, Walker's agents capture Mark who they find in the desert nearby.
She interrogates Mark, asking about Purdy's stolen laptop, and tells him that the Garde saved Sarah and destroyed the base. Walker seems understanding of Mark's reasons for coming to Dulce to find Sarah. She informs Mark that he is being hunted by the Mogadorian-loyal faction of the FBI and that putting him in protective custody would be akin to throwing him to the sharks. She allows him to leave without confiscating Purdy's Laptop or any of his other possessions. (The Fugitive)
Allying with the GardeEdit
Walker and her crew travel to Ashwood Estates and wait for a chance to strike before they witness Four take it over. They decide to make contact, but the Garde are initially suspicious. Walker tells them the history of the FBI involvement with the Mogadorians and information on MogPro. She wants the Garde to go with her to New York on the day that the Mogadorians are first introduced to the public to assassinate Bud Sanderson and expose Setrákus Ra.
Agent Walker travels to New York with some of her agents, John, Nine, and Sam. The group fight their way through Mogadorians to get to Bud Sanderson's hotel room. Sanderson, having missed two days' worth of MogPro injections, is in a bad condition and on the verge of suicide. Walker watches in awe as John heals Sanderson and begins to glow as he fights off the Mogadorian essence in his body.
Walker manages to convince the local police to aid the group through the crowded streets to get to the UN building where Setrákus Ra will be invited in for "discussions." On the way, Sanderson gives Walker dozens of names of politicians who are associated with MogPro and orders her agents to arrest them, or kill them if they resist.
At the UN building Setrákus Ra reveals himself to the public. However, a fight breaks out when Nine destroys his staff and his true monstrous form in revealed, causing panic. Walker and her agents take the opportunity to open fire at Ra, shortly after Ella's Dreynen stops his Legacies. Four is forced to stop the bullets after learning that, due to a charm placed on Ella, any harm to Ra will happen to her instead.
Walker is last seen trying to evacuate civilians before she is separated from John and Sam when the Mogadorians open fire on the City of New York. '(The Revenge of Seven)
Walker and three of her agents, including Agent Murray, survive the attack and make it to a military base. She later greets John, and informs him two things: Sanderson and MogPro are dead, and the progress report of the invasion. She also shows John a message from Setrákus Ra, saying that the Garde have 48 hours to surrender.
After receiving a message, Walker, Murray, and the other two agents join John, Sam, and Daniela to get Nine from Five. The agents, including Walker, think they should either kill Five or keep him custody. After John heals Five and Nine, the Hunter attacks New York. Walker calls in a pair of black hawk helicopters, and they open fire on the Hunter to no effect. After John and Daniela turn the hunter into stone, she talks to the U.S. President, who wants to discuss strategy with John.
Rogue FBI FactionEdit
After the death of Agent Purdy, Walker decided to turn against the Mogadorians. The Agents that are loyal to her, including Noto, form a faction of the FBI who ally with the Garde.
Walker approaches the Garde at Ashwood Estates and form an alliance. She shares all the information she knows about the Mogadorians plans and MogPro and they form a plan to kill the Secretary of State, Bud Sanderson.
Setrákus Ra and the MogadoriansEdit
Walker was initially assigned to aid the Mogadorians in their hunt for the Garde, in return for weapons and resources that would benefit the future of America. She changes her opinion and allies herself with the Garde to fight them. She tries to kill Setrákus Ra during the invasion of New York City, but is stopped by Number Four, who knows any harm caused to him will happen to Ella.