The Doctor has regenerated but it hasn't gone well. He's mentally unraveling and needs a place to rest beyond outside influences. Unfortunately the Master has laid a trap for the TARDIS that denies the Doctor undisturbed recovery time.
Did You Know?
(Sarah Jane Smith) and Louise Jameson
(Leela) were each asked to reprise their companion roles in order to ease an audience, many of whom had only ever known Tom Baker
in the character, into a new Doctor. Each of the actresses declined. See more
What's a Zero Room, anyway? Doctor said something about non-interfaces.
I suppose it's some sort of neutral environment, an isolated space cut off form the rest of the universe.
He should have told me that's what he wanted. I coulda shown him Brisbane.
Featured in A New Body at Last