Angel Resendiz aka The Railroad Killer criss-crossed the US by freight train in the 80s and 90s, choosing his victims at random, before he was executed by the State of Texas in 2006. Before his death, Resendiz spoke to journalist Alex Hannaford and claimed, on tape, to have killed more than he had taken the blame for. The authorities said Angel Resendiz was lying in an attempt to delay his own death. But, haunted by the crackly interview tape, Alex is determined to investigate. Then a letter arrives from a woman serving life in prison for her husband’s murder — telling him that Resendiz once confessed to that killing too.