In a future world, Gardai Inspector Declan McGuinness retires and meets a man from his past, Spencer Noonan. Noonan wants to give him a special retirement gift--a Rhine River cruise. But there's one catch: Declan has to find the person among the cruise guests who wants to kill Noonan. Declan agrees but needs to get a PI license and go undercover with his wife, Honey.

The cruise is lovely, but the guests are a strange mix. A subsequent murder and attacks lend credence to Noonan's fear, but it's not clear who the real target is. Working with the Gardai, Declan chases down clues involving a mystery robot, a shadowy life-extension project, and an insurrection in Kenya.

By the end, Declan gets his permanent PI license, and Noonan makes a fateful decision for himself and his son.