The Lost Boy - SJA 1.5

In which the TV news broadcasts a plea from the parents of a missing boy - and he looks exactly like Luke Smith. Ashley Stafford has not been seen since getting on the Bubble Shock bus five months ago, and now his mother and father, Heidi and Jay, are appealing for the public to help find him. Sarah asks Mr Smith to scan Luke, and he confirms that his DNA matches that of Ashley. The computer is unable to say why this was not identified before.
At the Jackson household, Alan has been threatening to move away from the area, concerned by Maria's new lifestyle. He relents on the condition that she tells him what she is up to at all times. Mum Chrissie then arrives, claiming that she has called the police to report Sarah. They arrive and take Luke and Sarah away. Luke is returned to his parents, whilst Sarah uses her UNIT contacts to gain her release.

The experience leaves Sarah bitter, regretting having opened her heart to the boy. This bitterness extends to his friends, as she begins to shun Clyde and Maria. Mr Smith recommends she take up an investigation to take her mind off things. Sarah goes to the Pharos Institute, run by Professor Celestine Rivers. Here she meets the obnoxious child genius Nathan Goss, and witnesses him using a headset derived from alien technology to boost his telekinetic abilities.
Luke, meanwhile, has discovered his "parents" to be cruel and domineering. Maria and Clyde are forbidden from visiting him, and he is locked in his bedroom. Mr Smith asks Sarah to steal the headset so that it can be studied.
It transpires that Heidi and Jay are Slitheen, their compression units now enabling them to fit into much slimmer bodies. Nathan is also a Slitheen - the child whom Luke had previously encountered when the Slitheen infiltrated his school. They have abducted Luke on the orders of the mysterious Xylok. When Clyde goes to the attic and attempts to get Mr Smith to help him he discovers that the computer is Xylok. It dematerialises him - imprisoning him within its systems.

The Xylok is an alien crystalline lifeform, which crashed to Earth centuries ago. Part of it was given to Sarah to help create Mr Smith, having been found after the eruption of Mount Krakatoa. It plans to release the rest of its kind from the depths of the Earth's crust by destroying the planet. Luke's mental abilities far surpass those of Nathan, and he will be used to shift the Moon out of its orbit to collide with the Earth. The headset will allow him to do this. Clyde is able to tap into Mr Smith's systems and contact his friends via the mobile phone network. Computer Programmer Alan has developed a virus which can delete any computer system. He joins Sarah and Maria as they go to the Pharos Institute to stop the Slitheen. They manage to convince them that the Xylok intends to kill them along with everyone else. They give Sarah a teleport device which enables her to return to the attic where Luke is causing the Moon to approach the Earth. She calls upon K9 to attack Mr Smith, then uses the virus to wipe its memory. She gives it a new set of directives - that it must always defend the Earth - and it helps restore the Moon to its orbit. The Slitheen return to Raxacoricofallapatorius.

The Lost Boy was written by Phil Ford, and was first broadcast on 12th and 19th November, 2007.
It marked the conclusion to the first season of The Sarah Jane Adventures, and linked directly to the opening story. As such, we have the return of the Slitheen - including the child previously known as Karl. There are also links back to the pilot episode, as it references how Luke had been created by the Bane. Sarah's closing monologue is the same as that from the pilot episode.
Not only does Mr Smith, voiced by Alexander Armstrong, have more of a role to play, it turns out that it is the villain of the piece.
K9 (voiced as usual by John Leeson) makes another cameo appearance, having been seen briefly in the pilot.
The Slitheen no longer have to confine themselves to bodies of a fuller frame, but they are still out for revenge. The child had previously seen his father killed because of Sarah and her friends. One very minor gripe for this first season is the similarity of the threats. In the first story, the Slitheen had targeted the Sun rather than the Moon, and in the Trickster story the Earth had been threatened by another collision - this time a comet.

The main guest artist is Floella Benjamin as Professor Rivers. She came to fame for her children's TV work, including Play School and Play Away. A Liberal Democrat life peer, she is now a Baroness and was awarded an OBE in 2001.
The human Slitheen are played by Jay Simpson (Jay) and Holly Atkins (Heidi). Nathan is Ryan Watson. Their natural Slitheen counterparts are Paul Kasey, Ruari Mears and Jimmy Vee.
Overall, another very good episode of the spin-off series. The first episode is really quite dark and unsettling. The standard has been high throughout. The Sarah Jane Adventures managed a consistent level of quality which even the parent programme could rarely sustain.
Things you might like to know:

• In the police station we see Sarah's UNIT file - and it contains a photograph of her from The Monster of Peladon. Quite how UNIT could have obtained a picture taken in Aggedor's temple on an alien planet is never explained. Surely a photo from one of the half dozen UNIT stories she appeared in would have been more sensible.
• The UNIT dating conundrum is referenced as the file fails to pin down when Sarah was with them.
• The story title was deliberately chosen to mirror the book by Dave Pelzer, who wrote a series of autobiographical works based on his abusive childhood. 
• The Pharos Institute was named after the Pharos Project which appeared in Logopolis.