DOCTOR: That cybermat's happened, Harry. Kellman! LESTER: He's lying. Now Sarah and Harry are down there, and without that pentalium drive I can't bring them back. SARAH: What is it? STEVENSON: Sabotage? The Doctor transmatted us to get rid of the poison. Why have you come to Voga?
Plan: A: The Doctor; Q: Who sends Sarah and Harry to Voga to cure Sarah of the Cybermat's poison? A: Kellman's sabotage; Q: What is the reason the Doctor is unable to bring Sarah and Harry back? Summary: The Doctor transmits Sarah and Harry down to Voga to cure Sarah of the Cybermat's poison but Kellman's sabotage means he is unable to bring them back.