Sam Tyler (John Simm) is an ambitious young detective determined to keep the streets of 21st Century Manchester safe. However, the hunt for a serial killer becomes a personal vendetta when Sam suspects his girlfriend has been kidnapped by the very man he's tracking down. But after a near fatal car accident, Sam wakes up, dazed and confused, in 1973, struggling to understand what's real. Has he gone back in time? Is he in a coma? Or has he simply gone insane? His new boss is hard-nosed DCI Gene Hunt (Philip Glenister), a man who gets results by trusting his gut instinct and using a 'fists first question later' policy. Thrown head-first into this new world, Sam faces some of the hardest cases he has ever known. He has no idea why he is in 1973, but maybe if he can work out the reason, he can get home...