Here to give my two pence on Sam’s suicide I guess? I’ve got a lot of feelings and nowhere for them to go.
DCI Sam Tyler clearly has somewhat of an “I can fix him.” problem about the met police. He’s on a doomed one-man mission to singlehandedly change the police force and has spent his life working himself into a position where he can make a difference.
Except nothing really changes, at least in 2006. The world keeps turning whether he’s in it or not.
In 1973, the world he’s created inside his own head (or at least, that’s what he thinks and what we think by the end of Life on Mars. I have not finished Ashes to Ashes yet so y’know, I don’t know what’s REALLY going on) he MATTERS. When he tries to make a difference, things actually change. He can try to change every mistake he ever made, he can try and fix the future before it happens.
I really think that’s what prompts him to ‘go back’. The fact that there’s only one world that he’ll ever matter in, and it’s not even real.