"You can't -- you can't just keep me!" objects Andrew, having a bit of a fit over the knowledge that the Master can, in fact, do exactly that if he doesn't find a way out of this situation before the Time Lord has a chance to take him 'to more secure quarters.' The TARDIS's warning about the Master flashes through his mind, not that it would have done him much good even if he'd listened to her and properly made friends with the Doctor like she wanted.