Continuity mistake: At the end of episode one, when the Doctor and Taron spray paint onto the invisible Dalek, they use two different colors. At the start of episode two, the Dalek is suddenly black and painted on all sides.
Continuity mistake: When Wester - an invisible Spiridon - is treating Jo's arm, his shadow can be seen.
Continuity mistake: In episode five, Jo's hairstyle changes. She has one hairstyle in the bulk of the episode, which was filmed in the studio. And a different one during the "Plain of Stones" scenes, which were shot on location.
Continuity mistake: In the very first scene of the story, Jo is holding a gun as she opens the TARDIS doors, but when they come into the console room, she has no gun and is using both hands to support the Doctor.
Answer: TARDISes are generally available for properly authorised use on Gallifrey; they're not usually assigned to a particular Timelord on a long-term basis. The Doctor stole his when he left his homeworld.
Tailkinker ★