When the Sky Falls, Or, A Is for Adonis by Phil Earle

It's 1941, and Joseph has been packed off to stay with Mrs F, a gruff woman with no great fondness for children. To Joseph's amazement, she owns the rundown city zoo where Joseph meets Adonis, a huge silverback gorilla. Adonis is ferociously strong and dangerous, but Joseph finds he has an affinity with the lonely beast. But when the bombs begin to fall, it is up to Joseph to guard Adonis's cage should it be damaged by a blast. Will Joseph be ready to pull the trigger if it comes to it?