Who is Mr. Lamb? How does Derry get into his garden?

Mr. Lamb is an old man who lived in a big house with a huge and beautiful garden. He had lost one of his legs due to a bomb explosion and it had now been replaced with a tin leg. He liked to talk to people and make them his friends, and so, he kept the gates of his garden always open.

Derry was a fourteen-year-old boy who was low on self esteem and liked to stay alone. Considering the garden to be empty, he jumped over the wall to hide away from the rest of the world.