There is much fun to be had with trying to needle down your exact genre - see this example from my current sig:
near-future SF noir
near-future - i.e. not set in a completely alien future world
SF - because the main plot incidents and much of the surrounding elements are SF
noir - because of the general tone and atmosphere being aimed for
If I wanted to be really specific about the genre, I would have to throw in the following phrases:
crime - the two main characters are detectives trying to solve a crime / series of crimes
mystery - the main plot is a mystery the detectives are trying to crack
thriller - the major plot incidents are framed within action sequences and there is an overall pace being aimed for
Put all that together and you get this huge mouthful:
near-future SF noir crime mystery thriller.
It's pretty accurate, but it's actually not all that useful to either readers or agents / publishers.
Let's break it down, then.
Near-future and
noir aren't genres - they're just descriptors. So let's put them to one side.
Crime,
mystery,
SF, and
thriller are genres, but which one is the main genre here? SF trumps all of them in terms of setting reader expectations - because if you said it was crime or mystery, then readers expecting a police procedural could be sorely disappointed by the SF elements. I'd say the same for any other non-real elements, like paranormal, fantasy, UF, etc.
I think of this as a bit like saying whether a meal is vegetarian, vegan, whatever. It doesn't matter what's actually in there, but you need to know that high level stuff up front. But simply calling it
SF is a bit like calling a guitar band "rock". It may well be accurate, but it's so vague as to be useless. We need to narrow it down a bit more.
So which of the other genres is most relevant here? While there is a mystery at the heart of the story, it's not the driving force of the plot. Yes, the detectives want to uncover what's going on, but the reader often has more information than they do. So on that basis I would say not mystery.
While the mystery the 'tecs are working out is to do with a crime, and crime(s) instigate and propel the main plot, I am unsure whether this is the right genre tag. It's a multiple-POV story, and while the major ones are the detectives, there are plenty of other POV chapters and story threads outside the police.
Thriller is a good catch-all term for action-heavy stories, but what it really implies to me is a tone. Is it an exciting read, or at least intended that way? That's certainly what I'm going for, so I think this is an appropriate tag.
That leaves gives me
SF thriller. I'm reasonably happy with that, given that such a description almost never exists in a vacuum. It will always be accompanied by other materials - a query letter, back cover blurbs, etc. - and those should help bring out the mystery, the near-future setting, the crime elements, and the noir atmosphere.
... not changing my sig line, though. Too lazy