Sam receives a phone call from Frank Morgan and it seems the solution to his quandary is clear. If he brings down Gene Hunt, he can get home.
When Sam finds Gene, he and the rest of CID are looking at a dead miner. All roads lead to Leslie Johns, a notorious cop-killer that they believe is planning a heist on the train that transports the colliery wages. Gene is determined to head the investigation and put Johns behind bars, and so devises a plan that involves going undercover to infiltrate the gang of criminals.
As Sam questions the dubious ethics behind Gene's methods, he meets Morgan one-on-one. What Morgan tells Sam turns his world upside down. He claims that Sam is on transfer from Hyde, sent to Gene's department to surreptitiously obtain enough dirt to destroy Gene's career. Sam was injured on the day of the transfer and Morgan deduces that he must now be suffering amnesia about his former identity. His real name is not even Sam Tyler: this was a pseudonym created as part of his fake past life. It seems that Sam's 'home' isn't 2007, but 1973 and down the road as a DI in Hyde division.
Sam is in turmoil and has little time to work out who to trust as he and his team head into lethal danger. Gene is with Johns's gang, but Sam, Annie, Ray and Chris are all aboard the train. When it's hi-jacked and their cover is blown, Johns opens fire, and it looks to Sam like only Morgan can save them. As Sam leaves the others to find help, he promises Annie that he'll return.
But when Sam heads down the railway tunnel and meets Morgan, he opens his eyes in 2007. He's awoken from his coma and it seems that Gene and his 1973 world existed only in Sam's fevered imagination. But Sam is haunted by the promise he made to Annie, and determined to find a way back....
