DCI Sam Tyler finds himself back in 1973 after he wakes up from an accident that occurred in 2006.  Tyler discovers that he is a DI assigned to work under Gene Hunt.  Tyler investigates a series of murders that have been committed using the same MO in both 1973 and 2006.  Personalities and cultures clash when little attention is paid to forensic science (in 1973).  Tyler believes that suicide is the answer that will take him back to 2006 and is stopped, by Annie Cartwright, from jumping off of a building in order to test his theory.