DCI Sam Tyler's bad day just keeps getting worse. His case against a suspected serial killer has collapsed and his girlfriend and colleague Maya, has been kidnapped by the real killer. Worse is to come, he is knocked down by a car, when he wakes up - he appears to be in the year 1973. Confused, he's convinced he either dreaming or hallucinating and he's finding it difficult to believe all around him is real, including his new fellow officers. Sam discovers there is a link between a murder committed in 1973 and the serial killer who has kidnapped Maya - in 2006.

Sam, 's policing method from 2006 is causing conflict with Gene Hunt, his DCI who, 's policing method is rooted firmly in 1973. Unable to determine whether he really is in 1973 or a coma, he gets on with his job. When Kim Trent - high profile criminal is arrested, Sam discovers that Gene has planted evidence on him to secure a conviction, Sam intervenes and releases Trent to Hunt, 's fury. Sam argues that even Trent has human rights, Gene tells him he, 's never fitted up anyone who didn, 't deserve it. Between them, they set out to nail Trent using Gene, 's unorthodox methods and Sam, 's 21st century policing methods.

Sam is called to a murder at a textiles factory - which he is shocked to discover will be his own home in the 21st century. He puts his knowledge of forensics into use to find the killer, but Gene has a simpler approach - the first suspect to speak did it. As battle lines are drawn across CID, it becomes increasingly clear that the Seventies method of detection may in this case be right.

Sam discovers many of his colleagues are taking bribes from a local gangster, and resolves to put a stop to police corruption. However, a skeleton in Gene's cupboard makes him reluctant to join the crusade, and his fears are underlined when a young woman mixed up in the case meets a grisly end. The 21st-century detective also can't resist tracking down his mother, who is facing money worries.

When a Manchester United football fan is murdered, police suspect a rival City fan's to blame. The incident raises fears of a riot between supporters of the two teams, whose derby match is taking place at the weekend. Sam, Gene and WPC Annie Cartwright go undercover to gather evidence. But Sam worries they'll fail to find the killer before Saturday's big match. Meanwhile, Sam's relationship with the young son of the murdered man brings memories of his own father flooding back.

Sam hears his mother's voice saying goodbye, and worries that doctors in 2006 are about to turn his life support system off. When a hostage situation crops up, he becomes convinced that resolving the crisis without a single casualty will cause him to wake up in his own time. But Gene is determined to go in with all guns blazing, putting everyone's safety at risk.

A drug dealer dies while in police custody and Sam suspects a cover-up within the unit. He orders a full investigation, though it seems none of the other officers is prepared to help. To Gene's relief, the pathologist's report appears to put everyone in the clear, but when the truth about the criminal's demise emerges, it's up to the 21st-century cop to decide whether to reveal it.

The investigation into the murder of a bookies' clerk leads the team to 29-year-old Vic Tyler - who Sam is shocked to discover is his own father. He realises the time when he and his mother were abandoned is coming up, and desperately tries to persuade the small-time gambler not to leave his wife and child. Meanwhile, Gene sees an opportunity to bring down a crime syndicate.