George, Timmy and the haunted cave - Enid Blyton

The first prequel sees George, aged nine, cutting her hair short, refusing to answer to the name Georgina, and discovering Timmy as an abandoned puppy on the moor. Their first adventure together has them on the trail of the post office robber, who has hidden his haul in a cave on the beach. George and Timmy discover this when they set up camp in the cave, only to be disturbed by someone digging at the front of the cave. But, before the robber can unearth his haul, the cave is filled with mysterious ghostly noises. George and Timmy are terrified - and so is the robber, who makes his escape, without the stolen goods. George fetches the police, the thief is captured and the mysterious cave noises are discovered to have been made by the post office mistress's parrot, who escaped during the break-in.