City Beneath the Sea - Episode Guide

Science journalist Mark Bannerman and his youthful assistant Peter Blake are covering a story on board a submarine when the vehicle is stolen by a former U-boat commander.

Swendler evades capture by the Royal Navy and pilots the stolen submarine to a mysterious underwater city.

Bannerman and Peter are set to work in a laboratory in the undersea city, alongside several kidnapped scientists.

Peter is rescued and brought back to the city, and the air circulation system is repaired. Professor Ziebrecken explains his plans for the conquest of the sea, and Bannerman makes a shocking discovery.

Ziebrecken plans to use the threat of a nuclear strike to secure his installation as world leader. Peter tries to get a signal to the surface.

Swendler arranges a fatal "accident" for Bannerman and Peter.

With his nuclear missiles in place, Ziebrecken makes his demands to the world's governments: surrender or be destroyed.