Lady Christina de Souza is a high class thief, and while making her getaway from a robbery,she gets on a London double-decker bus that the Doctor is also riding. Bad idea, since the next the next thing to happen was that the bus + passengers went through a wormhole and ended up on a nasty alien planet.
The Doctor and Christina are successful in routing all the nasty aliens and getting themselves, the passengers, and even the bus back through the wormhole to London. Once there, Christina asks the Doctor if she can hitch a ride with him, but he refuses, the reason being that his recent collection of companions had come to unhappy endings as a result.
Lady Christina de Souza was played by Michelle Claire Ryan (born April 22,1984)