Jim Backus, fresh from playing the millionaire tycoon on Gilligan’s Island, plays millionaire tycoon T.R. Hollister while Roddy McDowall, fresh from playing a Phil Spector-like music producer in The Cool Ones (1967), plays Phil Spector-like music producer Nate Ashbury.
Tony Randall plays Fred Miller, head of research for T.R. Hollister – and an effeminate neurotic on the verge of a marriage break-up.
Fred forces his wife, Vivian (Janet Leigh) – who suffers from aquaphobia – and children Lorrie (Kay Cole) and Tommy (Gary Tigerman) to occupy ‘The Green Onion’ – an underwater house he has designed and built two miles offshore – in order to prove its value to his boss.
A rock and roll band called Harold & The Hang-ups (with Richard Dreyfuss as their bass player) comes along to finish their recording session underwater, and when the US Navy picks up the sounds on their sonar system, they are sure it’s an invasion and rush a fleet of ships to the area to foil the enemy.
Also along to entertain the audience is a plot-moving seal and several blood-thirsty sharks which are fought off by sadistic, trained porpoises.