DOCTOR: Is that all? DOCTOR: The Master. He'd have destroyed Gallifrey, the Time Lords, everything, just for the sake of his own survival. His plan. SPANDRELL: Out into the universe.
Plan: A: The Doctor; Q: Who realizes the Master is planning to tap into the Time Lords' power source to extend his own life? A: Gallifrey; Q: What planet is the Master planning to destroy? Summary: The Doctor realises the Master is planning to tap into the Time Lords' power source to extend his own life, an act that will destroy all Gallifrey.