Jem is the deuteragonist and also the hidden main female antagonist of White Bear. She is portrayed by Tuppence Middleton.
After being chased by the masked man, Victoria meets Jem and Damien, two people getting supplies. The masked man kills Damien, who attempted to save Victoria and Jem, forcing them to go on the run. Jem explains a mysterious signal over television and the internet turned most of the population into dumb voyeurs who do nothing but record everything around them. Victoria and Jem are unaffected but are also a target for the 'hunters', unaffected humans who, with society's collapse, can act wantonly violent and sadistic. Jem plans to reach a nearby transmitter at 'White Bear' to destroy it and stop the signal's effect on the area.
As they travel, a man named Baxter picks up Victoria and Jem. Baxter is also unaffected, but drives them to a forest and holds them at gunpoint. Although Jem escapes, Victoria is tied to a tree and about to be tortured until Jem returns and kills Baxter. They continue travelling to the transmitter, while Victoria has visions of past and future events. When they reach the White Bear transmitter to destroy it, two hunters attack Victoria and Jem. Victoria wrestles a shotgun away from a hunter and fires at her attacker - only for it to spray confetti. The walls open to reveal an audience applauding after observing the escapade; Jem, Damien and the hunters are revealed to have been part of a charade all along. Victoria is strapped into a chair, while Baxter appears and explains everything: the girl Victoria assumed to be her daughter was actually a six-year-old schoolgirl named Jemima Sykes, whom Victoria and her fiancé, Iain Rannoch (the man from the photographs), abducted a few miles from her home. After taking her to a nearby forest, Iain tortured and killed Jemima while Victoria recorded his actions on her mobile phone. The 'White Bear', originally the victim's teddy, was a symbol of the nationwide search and murder investigation, while the symbol on the screens and on the hunter's mask was identical to the tattoo that identified Victoria's fiancé (who committed suicide in his cell before the trial). Having tearfully pleaded guilty and insisting she was 'under Iain's spell', Victoria was given a sentence the judge described as 'proportionate and considered' – to undergo this mob-recorded, poetic justice every day.
- It's interesting to note that Jem's name is very similar to that of Jemima Sykes, the little girl who was abducted and killed by Iain and Victoria. It could be that Jem's name is a sort of tribute to Jemima, and offers some poetic justice, as Victoria is being tortured by Jem on behalf of Jemima.