The Medusa Protocol by Rob Hart

 Medusa is the sequel to the equally engrossing Assassins Anonymous. The characters belong to a support group of professional hitmen (and women) who want to get out of the business. In this novel, Astrid has vanished and the rest of the group tries to track her down and bring her back. Turns out she's been kidnapped because someone wants a memory buried deep in her brain and will do anything to get it.

It's a compelling tale, told with a dark sense of humor. I can't wait to see what this now peace-loving group is up to next.