Klepton city

A city on an Earth-like planet's ocean floor was built by a group of Kleptons led by Klepton One. In the 30th century they attacked a Thain city, abducting many Thains in their flying machines and took them to their city to make them work as their slaves. The First Doctor, John and Gillian followed a Klepton in a repaired flying machine to their city, which they destroyed after freeing the slaves. (COMIC: The Klepton Parasites)