The Monkey Mountain Monster finds Lindsey a reluctant day-camper partly because most of the kids come from another school in her town of Hope Springs, but mostly because of mouthy Mona, who's a put-down artist extraordinaire and who's never without her gaggle of admiring girlfriends. Lindsey wants no part of it, but Mona has lured Lindsey's best friend, Caitlin, into her crowd of disciples -- which leaves Lindsey out in the cold.

To complicate matters, there's a mysterious monster roaming through Hope Springs. On a dare Lindsey agrees that she will sleep out in her backyard one night -- but when she finds out that Caitlin won't join her, she realizes she really is all on her own.