Alex Sparrow and the Furry Fury by Jennifer Killick
Catching the school's runaway guinea pigs is not giving Alex job satisfaction, but how can he find a bigger test for his and Jess's awkward superpowers? Jess is more worried about the bullied new boy, whose Mum runs the animal sanctuary. She volunteers at the sanctuary, but soon realises that something is very wrong; the animals are terrified. People report strange events: things missing, property destroyed, and the local squirrels have turned mean.
The police have no suspects. It looks more and more like a job for Agent Alex...