I don't really have an interest in cop shows. Most of them confine their characters to merely going through the motions with no real insight into how the crimes they investigate affect them. Those that take that kind of leap include shows like The Last Detective and A Touch Of Frost, which are made over in the United Kingdom and should be the template for how you make such a tired genre interesting. The original Life On Mars, which ran for two seasons on BBC One, gave this kind of character depth with a nifty little science fiction twist.
The show centers around Detective Chief Inspector Sam Tyler (John Simm) who, while investigating a killer in modern-day Manchester, suddenly finds himself sent back to 1973 Manchester after being stuck by a passing car in 2006. Unsure of whether he really is in 1973 Manchester or merely in a coma, Sam incorporates himself into a time completely different (in fashion and in crime-fighting) from the one that he came from. As he tries to discover the truth of why he is in 1973, his place of employment is now run by a completely different individual, Gene Hunt (Phillip Glenister), a thuggish, beer-guzzling kind of cop who has no problem saying what he feels or belting a suspect (or Sam) when he feels it's necessary.
Rounding out his team of co-workers is the slightly aloof Detective Constable Chris Skelton (Marshall Lancaster), the "Gene Hunt in training" Ray Carling (Dean Andrews), and the soft-spoken but strong-willed Constable Annie Cartwright. Of the group of people that Sam often has conflicts with, Annie is the one who is the most likely to dive into the rabbit hole with his rants about being from the future and 1973 not being real.
I couldn't really describe for you what this series is actually about. In one sense it is about Sam Tyler trying to figure out the why in his predicament. In another sense this series is about finding your place. Although there are many instances where Tyler wishes to go back to 2006, as the episodes progress he develops a close tie to his 1973 surroundings.