A thousand years after his first visit to the planet Artaris, the Doctor returns. The city of Excelis has grown, spreading a vast Empire throughout the globe. Science and engineering have provided a new Age of Reason. But the more things change, the more they stay the same, and once again death follows the mysterious Relic through the halls of the Imperial Museum. When the Doctor finds himself helping the Curator and the local authorities with this mystery, he finds himself crossing paths with a familiar face from Excelis' history —- but no-one lives for a thousand years, do they?