The Moray Rose was a deserted spaceship in a spaceway. In its prime, it was "one of the biggest and the best" luxury space cruisers. The Moray Rose famously disappeared. The Adrianus was its sister ship. The Fourth Doctor always wanted to know what had happened to it.
At some point, Inter-Galaxy Insurance, owners of the ship, sent two agents, Calvert and Micah, to check the cargo hold. When the Fourth Doctor and Leela arrived in the TARDIS, around the same time, they found the cargo hold was completely devoid of cargo. Calvert thought they were pirates. (AUDIO: The Evil One)