As the Earth Cargo ship C982 passes through hyperspace, it narrowly avoids a collision with the TARDIS, which lands in the cargo hold. The Doctor determines it is the 26th Century, as Jo sees a ship come alongside, shimmer, and change shape, becoming a Draconian Galaxy-Class Battlecruiser. The pilots Stewart (James Culliford) and Hardy (John Rees) send out a distress signal and get ready to be boarded. Hardy discovers the Doctor and Jo on board but sees them as Draconian warriors and arrest them.
On Earth, the President (Vera Fusek) and the Draconian Ambassador (Peter Birrel) accuse each other of attacking each other’s ships and violating the Frontier Treaty. Earth General Williams (Michael Hawkins) reports to the President that a mission to rescue C982 is ready. It was General Williams who started the original war and has never believed in the Treaty. Anti-Draconian riots break out on Earth.
Locked up in C982’s hold, the Doctor decides that a strange sonic hypnosis caused Hardy to see them as Draconians—his greatest fear. The creatures who actually boarded the ship were Ogrons, who stun the pilots and the Doctor, tie up Jo, take the ship’s cargo and the TARDIS. Jo wonders if the Ogrons are working for the Daleks, as they have before, but Ogrons are mercenaries and could be working for anyone. When rescued, the Doctor and Jo are accused of being Draconian spies, are locked up again, and taken to Earth. The Doctor denies this and tries to convince the authorities that a third party is trying to provoke a war.
The Doctor and Jo are helped to escape again, and then again by the other side, producing lots of cliff-hangers. Everything convinces the authorities on both sides to attack. A mind-probe backs up the Doctor’s assertions, but no-one believes it, and the Doctor is sent to the Lunar Penal Colony. Fake records from Sirius IV “prove” the Doctor and Jo are Sirian criminals, and an officer arrives to take them away. It is the Master (Roger Delgado).
On the Moon, the Doctor meets Professor Dale of the Peace Party (Harold Goldblatt) and on Earth, Jo recognizes the Master. Deciding it is better than staying in her cell, she agrees to leave with the Master on his ship. On the Moon, Professor Dale believes the Doctor’s story and tries to help him escape. They are betrayed in the air lock, but are saved from asphyxiation by the Master, who takes the Doctor to the Ogron home world. In the midst of an elaborate escape-attempt, a Draconian Battlecruiser arrives. Everyone is to be executed, but the Doctor says he has important info for the Emperor. The Draconian Captain decides to bring them before the Emperor, but the Master secretly calls the Ogrons.
The Doctor addresses the emperor as a Draconian noble, which he turns out to be, having been given the title by the 15th Emperor 500 years ago. The Ogrons attack and rescue the Master, but they leave one behind, thus proving the Doctor’s assertion. An attempt is made to bring Ogron prisoners to Earth as proof of the Master’s treachery, but they are attacked by an Ogron ship, and then an Earth Battlecruiser. But General Williams is now convinced that his attack on the Draconians was an error. Humans and Draconians work together against the Master and his Ogrons.
The Master is unable to hypnotize Jo, and she escapes. Williams is about to save the day when the Master shows up with Daleks. They want to kill the Doctor, but the Master wants to keep him alive for gloating. The Doctor escapes to the TARDIS, but the Master shoots him. Before he passes out on the TARDIS floor, he calls the Time-Lords, using the TARDIS telepathic circuit.
Roger Delgado was supposed to appear briefly in the sequel Planet of the Daleks, but he was killed in an accident on a movie-set, with devastating consequences for everyone involved. My impression that the light went out on the Jon Pertwee years at that point may be subjective on my part, because these things were never filmed in order. Two stories later Katy Manning was gone, but her final story was already planned when Delgado died. Six stories later, Jon Pertwee was gone as well, and he has plainly stated in interviews that Delgado’s loss had a powerful effect upon him. I can’t help thinking of the death of Carrie Fisher.