CASTELLAN: The Doctor tried to evade security. A pleasure to see you again. Anti-matter cannot co-exist in harmony in our universe. The time factor involved leaves only one course of action open to us. Remove the Doctor to the security compound. MAXIL: They have their orders. DOCTOR: That's exactly what the High Council think.
Plan: A: the universe; Q: What was the anti-matter being trying to enter? A: the Doctor; Q: Who did the Gallifreyan high council decide to put to death? A: Gallifreyan; Q: What high council decided to kill the Doctor? A: the occurrence; Q: What did the Gallifreyan high council want to prevent? Summary: With a anti-matter being trying to enter the universe through the Doctor, the Gallifreyan high council see's only one clear course of action. They decided to put the Doctor to death in order to prevent the occurrence.