Based upon a true story, Alan Terry (Rupert Graves), a young, bright and wholly decent London tramp accidentally witnesses a mob execution. He gets away but leaves enough evidence for them to come looking for him. It also turns out that Inspector Matheson (Michael Gambon), in charge of the investigation is in cahoots with the mob. Billie Hayman (Annabella Sciora), a female reporter may be Alan's only hope. Can Alan keep ahead of the mob? Will Inspector Matheson be uncovered?