A slime monster living underneath Crystal Cove is cocooning anyone who gets in its way. Despite being warned not to continue investigating by their parents and authority figures, the gang attempts to solve the mystery. While investigating the caves under Crystal Cove, Daphne finds a locket containing a photo of a young couple. The gang realizes that the cocoon is made of a frozen yogurt-like substance from a new dessert shop, then realize that the new shop and the bank are near each other. After trapping the monster in the dessert shop, they reveal the monster is their science teacher who was trying to tunnel into the bank. Later, the gang receives a call from “Mr. E”, who says “the real mystery has just begun”.