Kill for Me, Kill for You

by Steve Cavanagh.

In an old Hitchcock movie, Strangers on a Train, two men discuss swapping murders — each will kill the other’s desired victim, but will get away with it since they have no apparent motive.

That’s the inspiration for a similar arrangement in this novel. Two women, each with a daughter who has been murdered. Each knows the man who killed her daughter but is getting away with it. They agree to avenge each other’s daughters; each will kill the other’s target, while the one with the motive has an alibi.