Mystery or Thriller or Both . . . .

I'm certainly no expert and from what I've seen, there are a few experts here.

From what little I've seen, though, a mystery would concentrate more on a particular crime and the process of solving it. Consider a murder - and a detective trying to solve it.

...A thriller would lean more toward the peril of the protagonist. The plot may feature a crime, but the plot would likely also revolve the greater consequences. Consider a murder - that is branded an "assassination" and could start a war.

From my perspective, that would be the difference.

Search the archives back; there's a whole lot of discussion about the differences between mystery and thriller. But:

A mystery is about solving whodunit. The crime occurs somewhere before the story starts or in the first couple of chapters. A detective or a detective-like person sets out to put the clues together to figure out who did it. The killer is not revealed until the end. The stories tend to be intellectually focused--the clues are being puzzled out. Usually you have one major murder and then maybe a couple others to cover it up. The motives for the crime can be ordinary things, like jilted lover, insurance money, covering up embezzlement, etc. They also, interestingly enough, generally DON'T make good movies (too talky, not enough action).

Thrillers are about paranoia, conspiracies, and heroes. They may not necessarily have a crime as the central focus of the story; the crime also may not be a common, garden variety one. There will tend to be a lot of action, possibly a high level of violence. The main character's life will be in great danger in the story. If it's a crime subgenre, the focus will be on catching the bad guy before he can kill more people rather than solving the case. A lot of bodies may accumulate in the story. The stakes will be a lot higher in a thriller: If this problem isn't fixed, something Really Bad Will Happen (crime thrillers tend to fudge this one quite a bit, which muddies the waters on the genre itself. All the other subgenres pay a lot of attention to the stakes). The stories are often complex, with many threads weaving into the main story, and it may even take a sudden left turn into something unexpected. Stories are more emotional. And if you see a best selling novel hitting the movie screen, it's almost always a thriller.

More about thrillers here: http://www.hackman-adams.com/articles/index.htm

For a very simplistic overview of the difference--and these are from observations of a non-published writer, along with hints from "how-to" books I've read--in the thriller, the murder, explosion, big bad thing about to happen, will occur at the end of the novel, and the story is how the MC will stop it, thus creating a lot of suspense. In the mystery, the murder, explosion, big bad thing about to happen, occurs at the beginnning, and the story is about the MC deductively figuring out who dunnit.

I warned you... these are overly simplistic, but I think you can apply them to most thrillers and mysteries. They'll overlap each other in some stories, and a lot of mysteries will have the MC trying to stop a repeat of the original "bad event" while s/he solves the mystery, and a lot of thrillers will have an inciting but smaller "bad event" that the MC might be trying to solve while s/he tries to prevent the real "big, bad event" from happening. But that's what I understand to be the major differences.