Colin and his family have just arrived at the lake. He's going to spend the whole summer swimming, canoeing, fishing, and just having fun. Best of all, he's finally going to build the treehouse he's planned for years. But his little sister, Katie, is always getting in his way, and of course his parents always side with her...On top of everything else, he keeps running into a strange bird, a killdeer, which seems to be following him around. Colin makes it his mission to find the bird's nest and learn as much about the killdeer as he can. It would be the perfect summer if he could find the nest and get his treehouse built, too...without Katie!