That same night, on Bannerman Road, Luke tosses and turns in his sleep, haunted by visions of the day he was born in the Bubbleshock factory. He awakens to see the woman who created him – Mrs Wormwood – standing at the end of his bed, calling his name. He hastily turns on the light but when he does so, she is gone.
The next morning Sarah Jane comforts her son, claiming what he witnessed was simply a nightmare, and that the real Mrs Wormwood did not know he had been called Luke, for she was destroyed before Sarah chose his name. Luke is still not convinced, claiming he has never dreamt before now.
There is a knock at the door and Sarah hurries to answer it. It is Rani, who is in a state of shock after discovering her mother has not returned home from work. Sarah and Luke hurry over to Rani’s house to ask Haresh about the incident but they learn little else, only that the shop floor was found covered in flowers – as if a struggle had taken place.
Sarah then takes Luke to Gita’s shop, where they are joined by Clyde. Sarah picks up an alien signal in the vicinity but the trace is too weak to identify which species. However, upon finding the cheque on Gita’s desk, Luke realises it is the Bane, the race that created him.
Hurriedly returning to Bannerman Road, Sarah speaks with Mr Smith, suspecting the cheque is a clue left by Mrs Wormwood for her to find. Sure enough, when Mr Smith scans the cheque, he discovers it is concealing an address, that of an abandoned warehouse. Sarah takes it as an invitation and vows to go to the warehouse. Rani, who has just arrived, demands to go as well, and Sarah agrees, although she tells Luke to stay behind in case Mrs Wormwood is after him. Clyde remains to look after his friend.
Soon Sarah and Rani arrive at the warehouse, whereupon Sarah recalls the last time she encountered the Bane, namely their plan to use the drink Bubbleshock to take over the Earth, and their attempt to overcome the 2% unaffected by the drink (of which Rani is a member) by creating Luke, a distillation of thousands of humans who visited the Bubbleshock factory.
Going inside the warehouse, the girls find Gita stood in the middle of one of the holding areas, seemingly in a trance. Rani rushes over to her as Mrs Wormwood arrives to confront Sarah, claiming that she has been watching Sarah and her friends for some time, hence her kidnap of Gita to get their attention. At last she reveals why she has called upon Sarah – she requires her help. She claims that Earth, and the rest of the galaxy, is under threat, and Sarah must help to avert disaster.
Soon two men enter and confront Mrs Wormwood, calling her an enemy of the Bane and ordering her to surrender or else be devoured. One of the men transforms into the true Bane form, a squid-like creature, but Mrs Wormwood uses her ring to distract it, allowing her, Sarah, Rani, and the transfixed Gita to escape.
As they flee down a corridor, the Bane uses one of its tentacles to grab Sarah’s leg, and it drags her back towards the holding area. Reluctantly Mrs Wormwood goes after her and manages to free her, and then the two women return to escape with Rani and Gita. Mrs Wormwood explains that after the Bane Mother was destroyed by Sarah in the Bubbleshock factory, she was thrown out of the Bane Kindred and is now hunted. However, she is fighting back; not to save her own life but to stop the Bane conquering the galaxy.
Returning to Bannerman Road, Mrs Wormwood releases Gita from her trance, and Sarah convinces her she had been sleepwalking. Gita appears to recognise Mrs Wormwood but she claims they have never met.
As Rani leads Gita home, Sarah takes Mrs Wormwood into her house, where Luke and Clyde are waiting. They all go up to the attic, where Sarah calls upon Mr Smith and tells him to place Mrs Wormwood in a containment vortex if she causes trouble. Rani arrives; in time to hear Mrs Wormwood talk about the legend of Horath and the Dark Empire.
Mr Smith explains to Sarah and the others that the Dark Empire was a period of tyrannical rule by a reportedly-immortal entity named Horath. Mrs Wormwood explains that Horath was defeated but not killed, so his body and consciousness were separated and hidden at opposite ends of the galaxy. The Bane have found his consciousness (which is being carried by a mercenary agent) and now they want the body, which is hidden on Earth. As revenge for being outcast, Mrs Wormwood intends to thwart their plans.
Sarah asks where Horath’s body is but Mrs Wormwood does not know. Mr Smith explains that the Tunguska Skull, a relic charting the legend of Horath and his demise, will be able to help them, but it is kept in the Black Archive, the repository of all alien artefacts deemed highly dangerous, an archive owned by UNIT.
Ordering Mr Smith to contain Mrs Wormwood, Sarah and her friends hurry downstairs, but again Sarah insists Luke must remain behind in case UNIT grow suspicious of her actions and come after him. She tells Clyde to look after him and orders them not to go near Mrs Wormwood. They agree and, after hugging Luke goodbye, she and Rani prepare to leave. However, before they go to the black archive, Sarah claims she must visit an old friend first.
Brigadier Sir Alistair Gordon Lethbridge-Stewart, in his home in the country, is visited by Major Kilburne, who has arrived to debrief him on his mission to Peru. However, the Brigadier is not interested, claiming in his retirement he is beyond missions, debriefings and the fools-errands he is sent on by UNIT as the official envoy. Major Kilburne protests, stating his official duty, but the Brigadier is again uninterested, instead claiming that UNIT has lost the benefit of common sense.
Kilburne claims UNIT has adapted to a more hostile age, but the Brigadier turns on him, claiming his encounters with Daleks, Cybermen, Autons and Zygons far outweigh Major Kilburne’s operations.
At that moment Sarah and Rani arrive, and the Brigadier welcomes them, as does Major Kilburne, who has read many of Sarah’s UNIT files. He bids the group farewell and leaves. Sarah, now in the Brigadier’s confidence, tells him of her intentions – she needs to break into the black archive. The Brigadier listens and when she reveals her plans, can only reply;
Back in Bannerman road, Clyde and Luke talk about parents, and how important they are. Luke claims that for this reason he must see Mrs Wormwood, and reluctantly Clyde agrees. Luke hurries to the attic, where Mrs Wormwood, almost tenderly, speaks to him about his life, and how difficult it is for him to fit in, to exist alone in the universe without kindred, just like her.
The Brigadier takes Sarah and Rani to the Black Archive, a massive security facility. Sarah and Rani hide in the back of the car so as not to arouse suspicion, and the Brigadier drives through the gates. He checks the coast is clear and finds Major Kilburne standing around. He manages to move him on, claiming that he is visiting the archive to research for his memoirs. Kilburne leaves and Sarah and Rani get out of the car. The Brigadier hands them a key card and stands watch as they hurry inside.
The archive is a massive warehouse of alien artefacts boxed up and stored away. Sarah uses a database to find the location of the Tunguska Scroll, and she and Rani hurry away to find it.
As Major Kilburne and the security guards monitor the CCTV cameras, the girls at last find the vault containing the scroll, and with the help of the Sonic Lipstick manage to retrieve it.
On Bannerman Road Clyde answers a call at the door, and discovers that one of the Bane is waiting for him. He calls up to Luke in the attic and Mrs Wormwood, fearing for her life, begs Luke to help her:
“Luke, I am your mother!”
In the Black Archive, Sarah and Rani are discovered. An alarm sounds and the two girls hurry back to the Brigadier, the scroll still in their possession. Major Kilburne and his men are soon on their tail.
Freeing Mrs Wormwood, Luke and Clyde flee into the back garden, but the Bane is hot on their heels. Mrs Wormwood tries to fend the creature off with her ring, really a Sonic Disruptor, but its power has been drained. The creature corners her as Luke and Clyde escape to the front of the house, where two more Bane are waiting for them.
Sarah and Rani return to the Brigadier’s car, where Major Kilburne and his men are waiting for them, guns aimed. Sarah zaps their earpieces with her Sonic Lipstick, giving her and her friends a chance to escape. They get in the car and the Brigadier speeds away, narrowly avoiding the closing gates.
In Sarah Jane’s garden, Mrs Wormwood cowers from the Bane creature, when it is suddenly blown to pieces…by Sontaran Commander Kaagh. Mrs Wormwood greets him and asks if he has the Consciousness of Horath. He claims it is hidden, but it is still safe. Mrs Wormwood is delighted.
“Then soon Sarah Jane Smith shall lead us to Horath and make us emperors of the galaxy. And she will crawl before me as we crush her world. Oh, the sweetness…of revenge.”