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.
- Actor Allusion: Mrs Wormwood introduces herself as "Wormwood, Mrs Wormwood", a play on the line "Bond, James Bond". Samantha Bond, who plays Mrs Wormwood, played Miss Moneypenny opposite Pierce Brosnan's 007.
- Alien Blood: When Wormwood saves Luke and Clyde by killing two Bane that were about to devour them, she uses her ring to make them explode into a shower of pale-yellow slime.
- 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.
- Black Site: The Black Archive, UNIT's "depository of everything that shouldn't exist on Earth but does anyway", is a rather difficult-to-miss, advanced-looking military base within sight of at least one road.
- Bond One-Liner: After the Brigadier shoots Major Kilburn (who was really a Bane):Sarah Jane: I always suspected Major Kilburn was a slimy creep.
- Boom Stick: The Brigadier uses a hidden gun in his cane to stun the Major.
- The Bus Came Back: The Brigadier returns for the first time in nineteen years. He last appeared on television in "Battlefield". His appearance in this story marks forty years in the role for Nicholas Courtney. Sadly, this would turn out to be his final appearance.
- Continuity Nod: When Rani asks how long the government have been aware of aliens, Sarah Jane says even Queen Victoria knew of them, referencing the creation of the Torchwood Institute in "Tooth and Claw". Rani replies, "Bet she wasn't amused", Rose Tyler made a bet with the Doctor that she could make Queen Victoria say, "We are not amused" and won.
- Disney Villain Death: Wormwood's form of demise when Kaagh pushes her into the portal, and they both plummet to their presumed deaths.
- Heroic Sacrifice: Kaagh pushes Mrs. Wormwood into the portal. It explodes, trapping them in another dimension
- 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.
- Luke, I Am Your Father: At one point Mrs Wormwood exclaims, "...Luke, I am your mother!"
- Never Mess with Granny: The Brigadier is an old man. This does not make him any less goddamn deadly with a weapon.
- Title Drop
- The Tunguska Event: The Tunguska Scroll was recovered from the site of the Tunguska Event, unsurprisingly.
- Uncertain Doom: Mrs Wormwood and Kaagh may have died from falling into the portal, but equally they may have survived and been trapped in the other dimension.
- We Can Rule Together: Mrs Wormwood says that Luke could be the ruler of the galaxy as her son.
- When I Was Your Age...: An unusually awesome example: The Brigadier gives one such lecture to a cheeky major who has the balls to suggest that they had it easier back in the old days.
- You're Not My Mother: Mrs Wormwood tries to convince Luke to go with her, saying she is his mother. Luke says his real mum is Sarah.