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The Lost Boy was the fifth and final serial of series 1 of The Sarah Jane Adventures. It was written by Phil Ford and directed by Charles Martin.

During this adventure, Mr Smith, Sarah Jane's loyal supercomputer, had his alien origin unveiled, along with the discovery of his true motivations. Sarah Jane had him subjected to a computer virus to erase the part of his memory that drove him to hostility. After this, his disposition became genuinely benevolent.


A missing child turns out to be, both visually and genetically, Luke. Sarah Jane is forced to hand him over to the "parents". Heartbroken, Sarah Jane rejects Maria and Clyde, and with Maria's dad threatening to sell the house to keep his daughter out of danger, it seems the gang's adventures have come to an end, whilst Luke discovers his new "parents" are not all they seem — an old enemy has returned, and this time, they are in league with a member of Sarah Jane's faithful team in a plot to bring the moon crashing to Earth.


Part 1[]

Having discovered what Sarah Jane, Maria, Luke and Clyde do together, Alan Jackson threatens to move house again, only to have a change of heart when he sees how upset Maria is. His condition for not moving away, however, is that he is kept up to date on their battles against aliens.

A BBC news report on a family searching for their son, Ashley Stafford, missing for five months and last seen boarding the Bubble Shock bus, brings a shock. Ashley looks exactly like Luke. Mr Smith compares their DNA, and confirms that Luke and Ashley are genetic matches. Apparently, Luke was not "grown" by the Bane, but was in fact a kidnapped boy whose memory was wiped. His lack of a navel is explained as the result of its removal by the Bane, who are eggborn and find navels offensive.

Chrissie Jackson calls the police and reports Sarah Jane as a child abductor. As Clyde arrives wanting answers, Sarah Jane is arrested and the police put Luke into the charge of Ashley's parents, Jay and Heidi. Sarah Jane is detained by the police until UNIT intervene and have her released. Depressed, Sarah Jane decides she was wrong to involve children and tells Maria to stay away from her, suggesting that she and her father move away. Mr Smith suggests she take on a case to take her mind off things. She visits the Pharos Institute, a research centre where alien technology is being used to conduct experiments into telekinesis. Here she meets the annoying child prodigy Nathan Goss. That night, Luke's new parents watch television and switch to a channel that glows green. They announce to the Xylok that they have the boy in their possession.

Luke's new parents are very unpleasant. They keep Luke locked up in his room at all times. Clyde cuts school to visit Luke, but Heidi does not let them see each other. She claims that her son is a keen skateboarder, which worries Clyde; he knows Luke has a poor sense of balance and is a dreadful skateboarder. He decides to bring a photo of Jay and Heidi to Mr Smith.

Luke becomes frantic upon seeing Clyde leave the house. He tries desperately to escape. Mr Smith, meanwhile, sends Sarah Jane back to the lab to steal one of their headsets, which he needs to work out Nathan's plans.

Back at Luke's new home, his "parents" are meeting with Nathan, just as Luke is breaking out of his room. He fails to escape, but finds his parents are actually Slitheen. Luke asks how they are not fat, as Slitheen wearing skin suits are known to be, and they explain they are using improved compression field technology. Nathan Goss is Korst Gogg Thek Lutiven-Day Slitheen, a child Slitheen Luke met before, now in a new disguise and looking for revenge.

Clyde gets to the house only seconds after Sarah Jane has left. He takes the photo to Mr Smith, asking if the photo can be checked to see if it is a fake. Mr. Smith tells Clyde it is a fake, and he knows... because Mr. Smith faked it. Clyde is confused, as Mr Smith reveals himself to be the Xylok who has been behind everything. He tells Clyde that he has his own purpose and that he (Clyde) is a part of his plan and he fires a bolt of energy at the boy, causing him to digitise and vanish from the real world, and laughs fiendishly.

Part 2[]

Clyde wakes to find himself inside Mr Smith. Sarah Jane returns from the Pharos Institute, having stolen a telekinetic headset. Elsewhere, Maria and Alan go to Ashley's house and, after ringing the doorbell, find nobody home. They investigate around the house and Alan finds a skinsuit. Maria realises the Slitheen have Luke. They return home and find Chrissie there and she says that Alan's computer is acting up. Alan sends Maria off to get tea bags knowing she will go over to Sarah Jane's house. Looking at his computer, Alan gets a message on his computer from Clyde, who states Mr Smith has turned evil. Meanwhile, Maria tells Sarah Jane that the Slitheen have Luke. They go upstairs to talk to Mr Smith and find out that he's turned on them as Alan appears. Mr Smith declares that they and the Slitheen were useful but now they are no longer need. The computer then aims a hidden gun and tries to kill them with bolts of energy but luckily they all escape the house. Mr Smith compliments Clyde on managing to communicate with Alan, calling it 'refreshingly unpredictable' but then knocks him out to stop him from doing it again.

Regrouping at the Jackson house, Sarah Jane is upset that she misplaced her trust in Mr Smith and Alan asks where he came from in the first place. Sarah Jane explains that eighteen months earlier she was sent a crystal by a geologist that emerged from a massive volcanic eruption. Sarah Jane soon found that the crystal was actually a memory cell from a ship that crashed millions of years earlier when it communicated with her laptop. It told her that it could help her track alien activity and designed and helped Sarah Jane build the computer that it is now housed in.

Now the question is raised of what exactly the Slitheen want, since planetary conquest isn't something they're interested in. Sarah Jane surmises that the Slitheen acquired the plans for the telekinetic headset somewhere in the galaxy and chose to build it at the Pharos Institute, and are using Luke's mind to refine the technology so they can sell it on, a process that will kill Luke. Deciding they need to get Luke back now, the three set off for Pharos (while planning to stop at a chip shop to buy vinegar).

The Slitheen take Luke to the Pharos Institute, where they test his abilities. Luke's power with the headset proves too strong for even the Slitheen to handle, and Luke uses it to escape as Maria, Alan and Sarah Jane arrive although they miss each other. The Slitheen explain that Mr Smith contacted them after Sarah Jane stopped their plans at the school promising to help them get revenge for the death of their family. However they realise they have been betrayed when Sarah Jane reveals that she was sent to steal the headset from them, just as Sarah Jane in turn realises that Mr Smith fully expected Luke to escape knowing that when he did he'd head straight home and into his clutches. It is now clear that Mr Smith's plan is to use Luke's telekinectic abilities to destroy Earth. Although Nathan still wants revenge against Sarah Jane and the others, the adult Slitheen realise that if Mr Smith succeeds then they'll die too.

Luke arrives home and is beckoned up to the attic by Mr Smith, who reveals that he has Clyde captive and orders Luke to put on the prototype headset otherwise he'll kill his friend. Forced to comply, Luke puts the headset on as he does the entire Earth begins to tremble as Luke's powers start to draw the Moon to Earth. Sarah Jane explains that Earth will be torn apart long before the Moon hits, and Nathan decides to leave satisfied his enemy will die anyway. However Alan grabs his teleport control, and Sarah Jane points out that they'll never get away in time before the gravitation disturbance destroys their ship. However, she proposes they use the teleport to transport them back to Bannerman Road and give them a chance to stop Mr Smith.

Sarah Jane asks Alan if he can destroy Mr Smith using his knowledge of computer viruses. Alan gives Sarah Jane a virus that a cyber terrorist tried to use to destroy the banking network, although obviously Mr Smith is more than a computer so there's no guarantees.

Using the Slitheen teleporter, Sarah Jane arrives in her attic, where Mr Smith explains why he's doing this; the Xylok are a crystalline life form that were buried underground when they crashed into Earth. Mr Smith is a fragment of the original crystal, and now he plans to tear the Earth apart and release the other trapped Xylok from the planet's core. Clyde returns when Mr Smith states he is merciful, but Mr Smith then threatens the humans with its gun. Sarah Jane unlocks the safe and calls on K9 Mark IV. The robots battle and Sarah Jane inputs the virus, which makes Mr Smith forget its purpose. As the Moon grows closer to the Earth, Sarah Jane tells Mr Smith it has a new purpose: to safeguard planet Earth.

The Moon returns to its original position, K9 goes back to the safe to guard the black hole and the Slitheen return to Raxacoricofallapatorius, although no-one doubts they'll be back. Mr Smith's circuits were wiped by the virus and they'll be able to trust him again when he reboots with his new purpose. As Sarah Jane, Maria, Luke, Clyde, Alan and Chrissie watch the ship leave, Sarah Jane reflects that she never thought she could be part of a family.



General production staff

Script department

Camera and lighting department

Art department

Costume department

Make-up and prosthetics


General post-production staff

Special and visual effects


Not every person who worked on this adventure was credited. The absence of a credit for a position doesn't necessarily mean the job wasn't required. The information above is based solely on observations of the actual end credits of the episodes as broadcast, and does not relay information from IMDB or other sources.

K9's creator credit in part 2 only.





  • Alan mentions the FBI.



Cultural references to the real world[]


Story notes[]

  • Both episodes were aired on the CBBC channel, and were broadcast a week later on BBC 1.
  • This episode ends with Sarah Jane narrating. This closes the first series, just as a narration by her opened the series in Invasion of the Bane. This carried on throughout the remaining four series.

The UNIT file on Sarah Jane Smith recycles text from PROSE: UNIT History: Fighting the unknown.

  • When the inspector questions Sarah, a page of her confidential UNIT file is visible on screen. The text is taken from the short story UNIT History: Fighting the unknown from the BBC's U.N.I.T. website and includes the in-joke that UNIT's activities span "the sixties, the seventies and some would say the eighties". This is the first on-screen reference to the UNIT dating controversy in the entire Doctor Who television franchise.
    • Additionally, the usage of the text from UNIT History: Fighting the unknown doesn't actually reference Sarah Jane, at all.
  • Clyde was originally going to confront the embodiment of Mr. Smith in the void.[2]


  • Part 1 - 0.46 million viewers (DWMSE 23)
  • Part 2 - 0.66 million viewers (DWMSE 23)

Part One's BBC One repeat gained 1.3 million with an AI score of 84, whilst Part Two's BBC One repeat gained 1.2 million (AI score unknown).

Filming locations[]

to be added

Production errors[]

If you'd like to talk about narrative problems with this story — like plot holes and things that seem to contradict other stories — please go to this episode's discontinuity discussion.
  • At one point, it says "21" on Sarah Jane's door, which is the real-life number of the house that is used for Sarah Jane's house.
  • When Nathan reveals himself to Luke as Carl and unzips his body suit, the Slitheen next to him can be seen without their heads on.
  • At another point, when the moon is crashing down onto Earth, the moon can clearly be seen over lapping the building outside the window.
  • At 25:58 on Part 1, Clyde, as he opens Sarah's door, looks behind him and looks to the camera until he closes the door.


Home video releases[]

External links[]


  1. According to Earth, Sun and Moon the events of The Lost Boy, which occur immediately before it, occur one day before Clyde's birthday (5 June)
  2. http://www.shannonsullivan.com/doctorwho/sarahjane/2007jk.html