Fred (Windsor Davies), and Ernie (Jack Douglas), are off on a weekend fishing trip to the country but when two busty young cyclists (Sherrie Hewson and Carol Hawkins) pitch their tent in the shadow of Fred’s caravan, he decides to go after an altogether different catch.
Meanwhile, Professor Crump (Kenneth Williams) and his glamorous colleague Dr Vooshka (Elke Sommer) are examining the remains of a mysterious Roman encampment, recently discovered beneath the site.
As the excavations continue, the weather gets progressively worse and the campsite grows increasingly treacherous – if the rain doesn’t get the campers, the mysterious holes appearing in the ground surely will.
For Daphne Barnes (Joan Sims), there is an even bigger discovery. After years of being estranged from her husband (Peter Butterworth), he is revealed to be none other than the down-at-heel camp handyman.