Bee's mom has a job in New York City for the summer, so Bee is being sent to summer camp. She's not excited about it. Being around other people is hard for her, plus she knows nothing about campfires, she's not a good swimmer and she's never even been in a canoe.

When she first arrives, things go pretty much as she expected. The other girls either make fun of her or ignore her, and the woods surrounding the camp give her the creeps: she keeps hearing elusive music coming from somewhere in the distance, and there's something unearthly about it.

But then Zippy comes on the scene -- an oddball like Bee, but with a lot more confidence and hard-won knowledge gleaned from many summers spent at this exact camp. And most importantly, Zippy has also discovered mysterious behavior going on at the camp: the older girls from the Hawks cabin are sneaking out to do . . . something. They're always exhausted, and their flashlight batteries are running out at an alarming rate. But their counselors are never woken up by girls sneaking out, no one on staff doing nightly rounds ever sees them outside the cabin, and even when they start doing a bed check at night, the girls all seem to be in their bunks.

Zippy and Bee are on the case, and with the help of an unlikely ally, they try to figure out what the Hawks are up to. But they soon discover there's more going on than just the usual summer-camp hijinks. How are the Hawks getting out at night? What is the deal with the (very cute) mysterious boy who seems to be working with the groundskeeper? Where is the distant music coming from? And what does the reclusive camp founder know about all of it?