Rex's parents have split up, he's about to make the daunting move to secondary school, and to make matters worse he has to spend his summer holiday on a remote and rainy Irish island - with lots of unruly sheep for company. The only upside: he'll be staying with his strange and brilliant Uncle Derm. Then Rex discovers Uncle Derm is about to execute his most hair-brained plan yet - to rob the island's travelling bank. Like the local legend of medieval Pirate Queen Grace O'Malley, Uncle Derm plans to redistribute the money to local needy causes on the island. And he needs Rex's help.