This is a movie where the director takes perverse delight in misleading you. Even the casting is meant to mislead you, since Steve Martin doesn't normally come to mind when you think dark, noir thrillers.
The first third of the film and the very end had me literally squirming in discomfort. I loved every minute of it.
A lot depends on surprises, so don't go offering spoilers, and watch out for spoilers that might ruin it for you.
Martin plays a successful dentist who makes one lapse in judgement, causing his life to spiral into a living hell with no imaginable solution. The title provides the unimaginable solution
It's described as a black comedy, but I really didn't laugh much at all, though there are some delightfully goofy throwaway moments.
The worst thing I can think of in a movie is the unbelievable coincidence. There are two in this movie, but I forgive them because the payoff is so worth it.