City in the Sea

Ben Harris (Tab Hunter), Harold Tufnell-Jones (David Tomlinson), and Jill Tregillis (Susan Hart) are aided by Rev. Jonathan Ives (John Le Mesurier) in their quest to escape the underwater city, where they face off against Captain Sir Hugh (Vincent Price), a tyrannical ruler who imprisons them until Ben can devise a means to stabilize the city's volcano, which is on the verge of destruction due to the prolonged exposure to the unique mixture of gases.