Christian the Lion by Anthony Bourke
"Do you hear that, little fellow?" Ace asked the lion cub excitedly. "You're coming with us!" It's almost Christmas and as two friends search for gifts in London they come across the most unbelievable sight - a lion for sale in the famous store, Harrods. Unable to bear the thought of leaving the little cub, Ace and John take him home and name him Christian. A year of fun and mischief later, Christian has grown up and Ace and John must find him a new home back in his native Africa.