Did you ever see that movie where the spy has a moment of clarity and retires before the job destroys his soul, but then someone (probably his girlfriend, but someone) gets kidnapped to use as leverage against him, so he’s sent off to do one last job, and it’s not a job he wants to do, but dammit, he’s a professional, and anyway, there’s someone counting on him to succeed. Killer Elite is that movie, except the spy is a British Jason Statham[1], there are more antagonists than just the kidnapper[2], and the someone is Robert De Niro instead of a girlfriend. So, you know, if you like that movie, this is a perfectly viable version of it.

[1] Odds are excellent that he is in fact British all the time, not only at this moment. Who can ever know for sure?
[2] Actually, this is a pretty meaningful distinction, and is the main thing that keeps the movie from being one you’ve seen multiple exact copies of before. So, yay that!