Karen is a supporting character introduced in Series 5, becoming a more important character with the progression of the series. A shy Scottish girl living in Wertham when The Storm hit, Karen was given the power of Camouflage.
When Rudy Two sees a vision of her in the future on a woolly jumper, or at least her power, he resolves to tracking her down and convincing her to become part of a gang of "real superheroes" along with Helen and Sam. Notably, Karen is responsible for the death of long-standing Misfits friend Tim.
In the future she becomes a villain herself along with the rest of the Jumper Posse, and is killed by Finn's Telekinesis. However, this timeline was prevented from happening by Jess, and without the formation of The Jumper Posse ever happening, Karen's ultimate fate is unknown.
Little is known of Karen. Karen's existence is hinted at, along with Helen and Sam, in Maggie's Jumpers which foretell the future in S5E1. Rudy Two determines to track down the three figures depicted on the jumper, of which Karen is one.
Karen first appears in S5E6 as an assistant for a group of young people with terminal illnesses. They are at the Community Centre and Karen is talking to the gang, introducing the patients. After they continuously ignore her attempts to continue talking, she backs up to the wall, activating her power. They turn around and think she has left, commenting on her apparent rudeness.
Later, she is seen playing chess with Lucas and notices strange behavior from Ben and Lucas respectively. After Lucas uses his power on Finn, Rudy, Jess and Alex interrogate the wrong patient about Finn and Karen catches them just in time before Alex does his "you know" and explains to them what has actually happened after seeing Lucas acting suspiciously with Abby whilst using her power.
She is present at the community centre when Lucas gives Finn back his life-force. She notices the jumper in Rudy and Finn's room and realizes it is her on the jumper.
With this knowledge, she approaches Rudy Two on the roof after his search for the third and final 'hero' on the jumper. She tells him that it is her and he excitably tells her that she's the final puzzle piece and that he will introduce her to Helen and Sam. Karen fulfils the prophecy that she will join the superhero team with Sam, Helen and Rudy Two, despite initial misgivings.
After Jess is sent forward in time, it's shown that Karen and the rest of the Jumper Posse have started murdering people for minor offences such as littering. When Rudy Two, Jess, Alex, Finn and Abby confront them, the Jumper Posse strike first.
After they kill Sam, Karen ambushes them in the community centre in a series of sneak attacks. Despite the fact that her power is the least offensive of the Jumper Posse, she stabs Finn, Alex, Abby and Rudy Two, successfully taking them on four against one until she reappears and Finn's telekinetic powers let him kill her with a thrown piano.
After this future is prevented, Karen's fate is unknown.