Readers around the world have fallen in love with the Senior League, five residents of the Diamond Retirement Home—Martha, The Genius, The Rake, Christina and Anna-Greta—who turn to a life of crime.

New owners have taken over the Diamond, making cost-cutting changes that have transformed the happy home into a dull and dreary place. The residents wonder if they wouldn't be better off in prison! Martha gets an idea: they shall commit a crime that will ensure conviction—some type of financial crime, a small coup of some sort. They will give whatever they get to the poor and elderly. If Robin Hood could do it, so can they!

What starts as a robbery attempt at a nearby luxury hotel escalates to art theft from a major museum, the culprits armed only with bolt cutters and high-tech walkers. The Mafia gets wind of these robberies, and suddenly the underworld has its eye on both the stolen paintings and the handiwork of The Genius. Soon the Senior League has both the law and the lawless at their heels.