Frank Perry is an institutionalized convict twelve years into a life sentence without parole. When his estranged daughter falls ill, he is determined he make peace with her before it's too late. He develops an ingenious escape plan, and recruits a dysfunctional band of escapists - misfits with a mutual dislike for one other but united by their desire to escape their hell hole of an existence. Much of the action takes place within the tunnels, sewers and underground rivers of subterranean London.