Tom and Stella moved from noisy, sunny Hong Kong to dull, rainy London. They used to have many friends, but in the new house they don’t know anyone. Out of boredom, Tom decided to unravel the secret of the neighbor's dog Harry. He regularly disappears for several days and often returns soaking wet, as if he had swum in a lake, although there is not a single body of water around. Tom and Stella spy on the nimble dog, and Harry leads them to a hole in the ground. This is not just a hole, but a well - an iron staircase leads down. Of course, the children descend - for a long, long time until they find themselves... in the bushes near a lake flooded with sunlight! Is there a reasonable explanation for this? Is the well so long that they ended up in Australia?