As John Thornton returns to civilization with Buck, a drunken miner attacks John Thornton and threatens to do him harm. Buck immediately reacts and kills the man. Later on, John Thornton is lost in some fast river rapids, and once again Buck saves his master's life by swimming to him with a tow line. On another occasion, Thornton makes a brag that Buck can pull a sled with a thousand pounds loaded atop it. Because of his great love for John Thornton, Buck finally succeeds in moving the heavy sled one hundred yards.