The Master tips his head, appreciating the scenery as the Doctor finishes undressing. There we go. This isn't entirely new to you, Doctor. You know how to be absolutely certain of your own right to command. Your wants.

The sight of the Doctor standing in front of him, naked, erect and stroking himself, sends a frisson through the Master, a shiver of appreciation that encourages his own erection.

He moves one hand to touch himself, in a mirror to the Doctor. The movement is deliberate, telegraphed.

Challenge him.