And there is exactly the reason the TARDIS didn't want Andrew talking to the Master. All the Doctor's memories are locked away inside his head (some more corrupted by data loss than others, granted), and here he is with the body of a Lilliputian and telepathic defenses that can only be described as 'stunted.' The former the Master can see for himself, but the latter...well, Andrew will have to hope he doesn't figure the latter out before the meta-crisis can stage an escape.

"No, you just need to satisfy your megalomania," he snaps. "Why you insist on thinking it's a good idea to try to rule the universe, I'll never understand."