The most powerful Key of Time has been divided into six pieces, which have been disguised and hidden within time and space. Now, the even more powerful White Guardian wants the Doctor to find the pieces. With the first piece successfully recovered, the Doctor, Romana, and K-9 track the second piece of the Key to the planet Calufrax. But when they arrive at exactly the right point in space, they find themselves on exactly the wrong planet – Zanak. Zanak, governed by the mysterious 'Captain', is a happy and thriving planet. Mostly. If the mines are depleted of precious metals and gems, the Captain simply announces a New Golden Age, and they are refilled. It's an economic miracle – so, obviously, something is very wrong...