It's a summer day so beautiful and peaceful that Hattie, paddling in her canoe in the middle of a lake, can't help but sing. In the deep water below, a creature is lurking. He's huge and green, with a long, long neck and he rarely leaves his lair. But on this day, he hears something sweet and inviting. He hears a song. What happens when the creature rises to the surface is nothing short of magical. Can a young girl and an enormous lake monster become friends? Together, can they save the beast from the frightened townspeople, who can't see beyond the creature's massive size?