2006. Police detective Sam Tyler and his team raid the house of Colin Raimes, their prime suspect in their hunt for a serial killer, only to find on interrogation he has a cast-iron alibi. Tyler's colleague and girlfriend Maya follows Raines, but is then, like the previous victims, abducted. A grief stricken Tyler is subseqently run down and left for dead in the road. When he opens his eyes, he appears to have travelled back to 1973. In his car, which is now a Rover V8, are papers explaining that he is on transfer from another police district.

Sam's once familiar police station is now a dark, primitive, frightening place, dominated by DCI Gene Hunt, a living, breathing personification of brash, politically incorrect policing of the era. While Hunt and his colleagues are bemused by Tyler, they are soon forced to cooperate on a murder case with baffling similarities to the one back in 2006.

Tyler finds the voices inside his television talking to him and commenting on his situation, a phenomenon he finds only slightly more outrageous than the police procedures of Hunt and his colleagues. Comforting him through his panic and bewilderment is WPC Annie Cartwright, a lone female voice in a male-dominated world, who admits Tyler "doesn't seem like the rest of them".

Tyler suggests checking the names of the suspects in his 2006 enquiry and finds a match with Colin Raimes, whose grandmother made a complaint to the police about the noise coming from the house next door. They raid it and find a now soundproofed murder site. As they arrest the killer, Tyler sees the five year-old Colin Raimes wave as the killer is driven away, and realises Maya was right: Raimes did know the killer, but they were one house away. And also, chillingly, that in thirty years, when he is released, he will kill again.

Tyler is suddenly confronted by a hypnotherapist, who claims he is speaking to him from his bedside in hospital and that whatever Tyler is experiencing is not real. Tyler prepares to throw himself off the roof of the building, hoping he will then wake from a coma. But Annie stops him, explaining the hypnotherapist was a friend of hers trying to help cure his delusions Tyler, still stuck in 1973 with no idea how or why, accepts her plea to stay.