Mad, mad idea. Quite original but derived from shows like Quantum Leap and Back To The Future. It's a real testament to the acting and script that although the basic plot is so silly you sit back and enjoy it so much.
Sam Tyler a modern CSI style techno cop is having problems with his girlfriend who happens to be a fellow member of the team he leads. Not only that he seems dissatisfied with his job and to cap it all said g/f has now been abducted by the serial killer he's presently hunting. Distracted by frustration and tearfulness he inadvertently wanders in the path of a speeding car and suffers a head injury which puts him in a coma. From Sam's point of view however he's been transported 33 years into the past, been demoted to DI and gets frequent visions of what's happening to him whilst he's lying on his hospital bed back in the future. Or at least that's one of the options he's exploring. Could be that he's hallucinating the whole thing. There's no way to know.
After a memorable first meeting with his new 1973 colleagues involving violence and an offer to cover up a possible drink driving offence on his part he finds out that the case they're presently working on is most likely the same guy he was after in the future. Confused? Try watching the pilot episode. It tells the tale much better than I ever could.