Tim O'Hara lived alone with his sister, Mary, in the town of Galway, Ireland. As he waited for the postman at the gate, a shaggy grey dog, almost as large as a Shetland pony, ambled up to his side. The dog looked solemnly over the gate, looking as though he were waiting for a special delivery himself. But today Tim has received a letter from overseas. It's from his Uncle Mike, who has struck gold in the Yukon and wants his nephew to come and join him there...