"The Call of the Wild" by Jack London
Large, strong and smart, Buck toughens to his new life. But even the toughest dog can be worn down by constant work, and after 3,000 miles of pulling sleds, Buck nears the end of his rope.
Cast away as no longer useful, Buck is acquired by greenhorns whose inexperience nearly kills him, but after being saved by John Thornton, he at last finds a man he can love.
Then on a remote gold-hunting expedition, Buck hears a call emanating from the woods and speaking to the wild heart of his distant ancestors. The lure of it almost balances the great love he bears for Thornton, but events take him away from his old life... and into legend.
Please be aware this book contains graphic descriptions of violence and animal cruelty.