Psychodrome by Jonathan Morris

Shortly after surviving the perils of Logopolis, Castrovalva and the machinations of the Master, the new Doctor and his new crew could be forgiven for wanting to take a breather from their tour of the galaxy. But when the TARDIS lands in a strange and unsettling environment, the urge to explore is irresistible... and trouble is only a few steps away.

The world they have found themselves in is populated by a wide variety of the strangest people imaginable - a crashed spacecraft here, a monastery there, even a regal court. And not everyone they meet has their best interests at heart.

With the TARDIS stolen, and the very environment itself out to get them, the travellers face an extremely personal threat. They'll have to work as a team if they want to get out alive... but can you really trust someone you barely know?