Ava Alexandra Hughes is 7 Years, 4 months and 15 days old. She's looking forward to her first day of Year 3 at Crabtree School for Girls. But there is a serious problem: Crabtree School is just too good. It's such a good place that the Lear 6 class from last year refuse to leave. Now those pesky eleven-year-olds are clogging up the whole school, and Ava is going to be stuck in year 2 forever and ever. Ava and her friends must come up with a plan to get the Year Sixes out, for good.