The Castor was a Century class spacecraft used for prisoner rehabilitation. Humans caught a dimensional traveller and used its ability to extract feelings and memories to draw out the evil from criminals. The traveller became so overwhelmed that it had to release some of the evil, which became a kind of dark angel. This evil entity killed all the people on the ship. The Tenth Doctor and Martha Jones discovered the ship adrift centuries later. (PROSE: Wooden Heart)

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