TV episode review
UK airdate 21 May 2010 (BBC One)

When Alex learns the identity of the young copper who's been haunting her, the pieces start to fall into place...

If you've not watched the final episode, stop reading this review right now – you need to experience this episode the way the creators intended (even if apparently there's 20 minutes of footage yet to be revealed).

Put very simply, Matthew Graham and Ashley Pharaoh have achieved what seemed the near-impossible: they've taken plot strands going all the way back to the very first episode of Life on Mars and provided an explanation that tracks with everything both Sam Tyler and Alex Drake learned about the world in which they're stuck.

We understand what happened to Sam after he returned to what can probably be described best as limbo; why Gene has always been insistent that no one can leave without his say-so; even the exact moment of Alex Drake's death, making sense of the season two cliffhanger.

The best thing is that all these revelations are threaded within a standalone cop show story, in which Ray, Chris and Shaz use proper police work to track down a group of diamond smugglers – at least until Jim Keats manages to lure them away from "Fenchurch East". Even then, to probably no one's surprise, they come and help Gene and Alex for the take-down.

Jim Keats's Satanic nature is sold not just by Daniel Mays' performance but little details like Chris, Ray and Shaz constantly descending as they enter Keats's kingdom (although the lift shot is perhaps a little over the top). The fact that he's not defeated, and Gene knows that a rematch is inevitable – and indeed, there are hints that he's not the first Satanic avatar to try to bring Gene down, and won't be the last – could be seen as depressing. But seeing Gene looking for a replacement for the Quattro and preparing to deal with the iPhone-seeking new arrival brings a wry smile.

Keeley Hawes' performance as Alex Drake came in for a lot of flack in the first series, but Alex's realisation that she really is never going to see Molly again is tear-jerking, and brings out the gruff compassionate side of Gene Hunt for their final farewell.

Inevitably there are a few loose ends but when you think of the number of series that end with a never-resolved cliffhanger, it would be churlish to complain too much. RIP PC Gene Hunt 6620; long live Gene Hunt, the Guv'nor! Pub? Pub!! Paul Simpson

VERDICT: 10/10