Mrs. Wormwood has been marked for death by the Bane due to the failure of her last attempt to invade Earth. Desperate, she reaches out to Sarah Jane & Co. for help. She tells them that the Bane were attempting to revive a godlike cybernetic entity called Horath, whose body and consciousness were separated at opposite ends of the galaxy. The Bane had found the consciousness and were seeking the body, which was hidden on Earth. Wormwood convinces Sarah Jane to find the body before the Bane do. The only clue to the body's location is the Tunguska Scroll, which is hidden in UNIT's Black Archive. Sarah Jane enlists the help of her old friend the Brigadier to break into UNIT's archive and steal the scroll.
It is revealed that Wormwood had allied with Kaagh, an exiled Sontaran, who had stolen the crystal containing Horath's consciousness. Taking Luke hostage, Wormwood forces Sarah Jane to give her the scroll. Wormwood, Kaagh, and Luke head to the village of Whitebarrow, where Horath's body is hidden. On the way, Wormwood tries to convince Luke that she is his rightful mother and that he should join her in ruling the galaxy. Using the scroll and the crystal, Wormwood creates a portal to Horath. She then betrays Kaagh and attacks him with her sonic ring. Sarah Jane, Clyde, and Rani arrive. Luke refuses to join Wormwood and returns to his mother. Kaagh, with a final "Sontar-ha!" tackles Wormwood, pushing her and himself into the portal, sealing it. Sarah Jane destroys the Scroll with her sonic lipstick.
- Badass Grandpa: The Brigadier is an old man. This does not make him any less goddamn deadly with a weapon.
- Beware the Nice Ones: The Brigadier is an old man. If the situation calls for it, he will kill you.
- This is also why he's one of the note few people allowed to carry a gun around the Doctor. He will only use it when there is no other option.
- Immune to Bullets: Subverted. The Brigadier finally gets his wish to meet an alien menace who isn't immune to bullets when he faces a UNIT Major who is actually a Bane in disguise.
- Title Drop
- The Tunguska Event: The Tunguska Scroll was recovered from the site of the Tunguska Event, unsurprisingly.
- When I Was Your Age...: The Brig to the aforementioned slimy Major.
- We Can Rule Together