Meet Pietro Brnwa, Italian-Polish Jew, aka Dr Peter Brown, intern in a run-down New York hospital, aka Bearclaw, ex mob hitman in a witness protection programme. When a patient in the hospital recognises him, he's in trouble. But a hitman doctor has a lot of skills to call on.
This is fast-paced, outrageous, moving, and chilling by parts. It's told as interleaved present day and flashback episodes, so by the climax, we know precisely why Peter is in the position he's in, and can feel sympathy for him, despite him being a hitman. And the finale is brilliantly outrageous (with a very cunning red herring that made me think I knew what the resolution was going to be, only for it to be wrong)
Also, second-best use of footnotes in fiction ever.