DI Alex Drake wakes up in the 1980s after studying Sam's apparent suicide. While there is some story about her trying to get home to her daughter (which she seems to conveniently forget about an awful lot), the series mainly focuses on her trying to figure out who and/or what Gene Hunt actually is; whether he is all in her head like he was Sam's or something else completely. After the series, what do we learn in the last episode? Everyone is dead and Gene hunt land is some sort of purgatory for its inhabitants to come to terms with their lives and subsequent deaths, or to put it another way, so that they can go on to the "afterlife" where they can rest peacefully, Ashes to Ashes, Dust to Dust... turns out the title is a bloody big spoiler.
If thought about after carefully watching the two last episodes of series 3 back to back, the purgatory which exists as a place for dead coppers to resolve their issues before ascending to heaven or being claimed by Keats and descending to hell goes further than we thought. Consider Tobias Ndbele in series 3, episode 7 — after speaking to Chris on a park bench when Chris allowed him to escape, he disappears into thin air with an exhale similar to the sound effect used when others pass on. Perhaps he was having trouble passing on because he felt guilt for the death of Tsitsi, who in his own words had "her whole life ahead of her". What if almost every case Gene Hunt's team are working on help one or more of the people involved — villains, innocent people, other coppers not on the team - to pass on, too? This makes Gene and his whole team all the more heroic, because not only are they working through their own issues they are helping others to resolve theirs too as part of their casework at the same time. The fact the suggestion of this being plausible exists enough in subtle clues points to high-quality writing is quite impressive. And yes, this means Summers shooting his younger self and becoming a villain didn't go unpunished — at some point offscreen, Keats claimed his soul too.
Why is Alex is introduced as a hooker and very sexual in season 1? Well, because in reality she's a very straight serious person, who would probably struggle to progress unless she were the cleanest of the clean. In Season One she believes everything to be a fantasy. She is living out a moral philosophy concept: if she won't face consequences for her actions, does she have to be good? If there's no long term consequences in society for her promiscuity and sleeping with a yuppie that looks like Rupert Graves, then what is the harm? Gene Hunt calls her out on it, and she doesn't care, because to her, it's all not real. In season 1 she still believes it's all a fantasy, so she is roleplaying, with the sexy outfits, because she thinks its all a fantasy and a game. The more real it seems to her, the less fantasy she behaves. Notice how after she fails to save her parents, the objectified/sexy aspect of her character drops and everyone seems to become more than a stereotype. Because they arent.
Once you know that Ashes to Ashes (2008) is in fact about dead or dying people living in a Purgatory created by Gene Hunt, having Richard Hammond meet the cast in a 2008 Children in Need feature is mildly disturbing, considering that in September 2006 he was in a high-speed car crash, leaving him comatose. Fortunately, things seem to have turned out all right for him.
Horror might be overstating it, but Alex leaving Gene blue balled in the penultimate episode is worse than it seems when you realise that in all likelihood every woman he's had sex with in the Copper Purgatory is a figment of his imagination, although he didn't know it at the time. A connection like that is a rare thing given the small number of real people; Chris and Shaz were lucky.
The choice Chris and Raymondo are presented with towards the end of the third series: to go and join Keats' team and do things his way. Ray almost succumbs to the temptation when several girls walk past him on the stairs and Keats mentions that Friday night is cocktail party night, then leads them through to a series of "out of order" elevators. Notice that not only are they already on the basement floor, but when the doors open the elevator is a VERY long way down and surrounded in white hot light. Offscreen, they decide to and do the right thing by returning to save Gene, Alex and Shaz's rescue attempt in a Big Damn Heroes moment. So in effect, Chris and Ray saved not only their colleagues but their own souls by coming back to stop the jewel heist thieves — if they hadn't Keats would have taken Chris and Ray to Hell, and possibly if Gene, Shaz and Alex had been shot he may have claimed them too.