sentences:  It was written by Douglas Adams, and featured some of his humour.In the serial, the tyrant Queen Xanxia (Rosalind Lloyd) and the Captain (Bruce Purchase) use the hollow planet Zanak as a spaceship that surrounds smaller planets, including Calufrax, the second segment of the powerful Key to Time in disguise, to plunder the planets' resources that help keep Xanxia alive.The Key to Time tracer points the Fourth Doctor and Romana to the cold and boring planet of Calufrax, but when they arrive they find an unusual civilisation that lives in perpetual prosperity.