Husband and wife Elizabeth (Sherilyn Fenn) and Joseph (Doug Jones) run and underground tournament of women fighting to the death for the pleasure of wealthy spectators. Each woman is brought to the tournament against their will, and kept in cells by the organizers. As added incentive, surveillance is kept on a family member of each woman. When the fighter dies, so does their family member. After the death of each fighter, the execution of that family member is shown via live feed for the others to see.
The film opens on a confused Jamie (Rachel Nichols) awakening in unfamiliar surroundings following a night at a bar. She quickly finds herself pitted against the menacing and imposing Sabrina (Zoe Bell.) Jamie tries to talk Sabrina out of fighting, but Sabrina informs her that resistance is futile, and reluctantly fight. Though Jamie is played up as the protagonist early on, Sabrina makes short work of her, and beats her to death in incredibly brutal and graphic fashion, and continues to tearfully do so well after Jamie is clearly dead. At this point, Sabrina (Zoe Bell,) takes over as the unlikely protagonist.
Sabrina has a target on her back in the eyes of most of the other fighters, as well as the guards. Most of women are in it strictly for survival and to protect a loved one. One woman, the sadistic Phoebe (Rebecca Marshall) takes pleasure from the fights, and goes as far to admit to an opponent that she couldn't care less about her parents, who are the ones she's supposedly in it to protect.
Sabrina does have her share of allies, including Teresa (Tracie Thoms) and Rachel (Rosario Dawson in a very minor role,) but in the end, Sabrina and Phoebe are the final two survivors.
After Phoebe finishes Sabrina's friend and ally Cody (Bailey Anne Borders) in particularly brutal fashion, Sabrina demands an immediate match with Phoebe, which is granted. Sabrina makes short work of Phoebe, who laughs maniacally until the final blow.
Just when Sabrina thinks it's all over, and she's won the tournament, a new fighter, Isabelle is introduced. Sabrina gives up, and lets Isabelle win.
Seemingly dead, Sabrina is taken to their morgue, where she reveals that she was playing possum, and kills a pair of morticians. She comes for Elizabeth and Doug, who have Isabelle held captive. After Elizabeth kills Isabelle, Sabrina kills Elizabeth and then Doug. She escapes the compound, killing most of the guards, including Kurtz (Bruce Thomas,) who was particularly antagonistic toward her.
Just as it appears as though Sabrina will escape the compound to reunite with her estranged daughter, she is shot and killed by a sniper, who turns out to be the man who lured her into the tournament after the two hit it off at a bar.