On their way home from the Isle of Wight Pop Festival, Jeff, Trev and Mick along with girlfriends Marty and Cathy decide to pitch a tent on private land. In the morning the land’s owner Rafe turns up and orders them to get off his lawn but changes his mind when one of the girls emerges naked from the tent. Rafe explains he only comes down to the house at weekends and lets them stay providing they redecorate his house. The squatters agree but once Rafe leaves they plot to organize a pop festival at the house. Attempting to raise cash for the venture, the men coerce their girlfriends into making a blue movie. When this proves disastrous Jeff goes to London and poses as a pop journalist in order to book the groups “Crazy Mabel” and “The Juicy Lucy” for the festival.

During World War I, a German U-boat sinks a British ship and takes the survivors on board. After it takes a wrong turn, the submarine takes them to the unknown land of Caprona, where they find dinosaurs and neanderthals.