Dale E. Basye sends Milton and Marlo to Snivel, the circle reserved for crybabies, for their latest hilarious escapade in Heck. Snivel is a camp—a bummer camp—a dismal place where it's always raining, and Unhappy Campers are besieged by swarms of strange mosquitoes that suck the color right out of them. Soon the Fausters discover that some Unhappy Campers have been disappearing. So after Marlo gets chosen for a special project and never comes back, Milton makes up his mind to find her and all the missing children.

Can Milton find his sister and get the heck out of Snivel? With the help of some new friends, his pet ferret, and Vincent Van Gogh's ear, he just might have a chance.