CODE NAME BANANAS by David Walliams

Eleven year old Eric spends his days at the place that makes him most happy: London zoo. And there’s one animal in particular he loves: Gertrude the Gorilla.
with bombs falling all over London Eric must rescue Gertrude.
Together with his uncle Sid, a keeper at the zoo the three go on the run but while hiding out at the seaside they uncover a top secret Nazi Plot