Billy, not quite four years old, is innocently playing in his own back yard at the seashore with his dog Teddy, his puppy Rover, and his baby sister Mary, when a ball drops over from the next yard and hits him on the head. Peeved, he sallies forth to find the offender and meets Jack (the heavy) the six-year-old owner of the ball. A scrimmage ensues and Billy gets the worst of it. He retires to summon reinforcements, sending Teddy to avenge him. Teddy does so to such effect that Jack begs him to call him off, and then vows vengeance. Jack's chance comes unexpectedly that very afternoon. On the beach is Olive, Jack's four-year-old sweetheart. Further down the beach is Billy, with his inseparable companions: Teddy, Rover, and the baby. Gallant Jack leaves Olive while he goes to buy ice cream. Quite innocently Billy comes up to Olive and makes such a hit that she strolls off with him, with Teddy, Rover, and the baby bringing up the rear. When Jack hunts them up, she sends him away. "I like Billy better," Jack scowls with anger, "That fellow is always making trouble for me." What will put Billy in wrong at home? Why, losing the baby, of course. Baby Mary, crawling around the rock that moment, offers a not-to-be resisted opportunity. Aided by the tempting ice cream, he entices baby toward him, then carries her off with faithful little Rover, to a big box further down the beach, and it becomes tightly locked. He intends to keep the baby there only a minute. Just then Mother calls him to go on an errand to buy a loaf of bread. Meanwhile, Billy and Olive, ready to return home, have noticed that baby is gone. The tide has risen and the box is gently floated off the rocks out to sea. When Jack gets to the beach, he sees the box floating on the water, beyond reach. While the policeman hunts for baby, followed by Billy and Olive, who trot along behind him as fast as they can, Jack is hiding among the rocks, crying in terror and remorse. The search brings them to Jack, whose tears rouse the policeman's curiosity. The latter makes him confess. Billy hears the confession. It is all simple now. "Go get the box, Teddy," and in Teddy plunges and swims out while the startled policeman runs for a boat, paying no attention to the children. By the time the boat is ready to be launched, Teddy has already reached the box and started for shore. In the excitement of the final rescue and reunion of the children, Jack is forgotten.