In The Waters of Mars, some of the dialogue between Captain Adelaide Brooke and her deputy Edward Gold suggest some kind of history between them. Firstly this exchange:
ED: Captain, With me.
(Adelaide and Ed turn their backs on Maggie and walk away.)
ED: I'm sorry, but it's an unknown infection and it's spreading. That demands Action Procedure One.
ADELAIDE: Do you think I don't know that?
ED: I think you need reminding.
ED: Well, at least I'm good for something.
ADELAIDE: Now and again.
ED: That's almost a compliment. Things must be serious.
And then Ed's haunting final words:
ED: Hated it, Adelaide. This bloody job. Argh. You never gave me a chance. You never could forgive me. See you later.
Is it ever revealed what exactly is the history between them? Perhaps in interviews or supplementary materials? It sounds as though there was some past unpleasantness, possibly prior to the Mars mission. Why is there such tension between them? What could she never forgive him for?