Max has unwisely borrowed Lili's bike, and a gang of three big kids snatch it from him. They even take his baseball cap! Now they want 15 euros to give him the stuff back.
Max shouldn't have borrowed the bike in the first place, and is really worried about what his sister will say. He lies and says he left it at Jérome's place. Then he gets up in the middle of the night and steals 15 euros from his mother's handbag. But when he goes to hand over the money the next day, the gang say they want more. And Max feels he's in too deep, and has to steal more money.
Lili finally saves the day by calling the cops, but I wasn't convinced by the ending - especially when the bad kids suddenly become good again, and offer to repair the damaged bike. In my experience, I'm afraid, this doesn't often happen. Not one of the best books in this series, and for once I felt the author was chickening out. Though I must say I'm perplexed about what better advice one could offer.