Sector V is spending the day at the beach, except for Numbuh 1 who hates the beach and thinks it's boring. He eventually leaves for the Treehouse and allow the others to enjoy themselves. While Numbuh 2 and Numbuh 5 swim, Numbuh 4 is buried to his neck in sand, and Numbuh 3 builds a sandcastle, declaring herself princess of the beach. Then, three bulky knights in sea shell armor who call themselves the Knights of the Round Towel destroy it by catapulting a bolder onto it and kidnap Numbuh 3.