Episode 225 is Ashes To Ashes (2008)

When DI Alex Drake is shot and lands in 1981, she comes face-to-face with DCI Gene Hunt, the relic of old-fashioned policing she read about in Sam Tyler's reports. Alex thinks she is in a coma and needs Hunt's help to go after Layton, the man who shot her in 2008. She is confident she knows the rules of the game, but with no contact from the outside world Alex has to contend with a terrifying possibility.