Secrets of the Stars

The scene opens up on a woman, Cheryl, visiting an astrologer to see her future in the stars. The man is a con artist, deceiving his customers to get money out of them, to which he finally admits this Cheryl, who has been visiting him frequently, when she reveals that she is using her mortgage money to pay. He walks to the window where a shooting star is heading exactly for his house, and he is possessed by an unknown being in front of the woman, and proceeds to possess her. Later, Luke, Clyde and Rani are visiting an exhibition with the freaky astrologer, Martin Trueman, as the event is free. Rani's parents, Haresh and Gita, and Sarah Jane also show up and each person fills in a card with their birthday and star signs on it and hand it to Cheryl who is now working with the astrologer. Luke is slightly upset given that he does not have a star sign as he was never born, but activated.

The show starts and Trueman begins to ask random dates and three people including Clyde stand up, as this is their birthday, although Clyde is unsure why he stood up. Sarah Jane tells him it is a trick of persuasion and she is skeptical about the entire show. Next, he asks for a person and begins to tell truths about her life, as the woman herself is shocked but enjoying the show. Sarah Jane then tells Luke, Clyde and Rani that the woman was a plant and that Trueman already knew her. Next, Trueman calls on Rani, and starts detailing that she has recently moved house and gives few details about her family. Rani is slightly amazed but not suspicious. Next, he calls on Sarah Jane, and begins detailing her travels with The Doctor in front of the audience, nobody but Sarah Jane, Luke and Clyde, and possibly Rani, could know of these stories and Sarah Jane is instantly suspicious. Trueman then predicts her downfall.

On the way home, Clyde encounters Trueman, who hypnotizes him to walk to his house and hypnotizes him to become his slave. In his trance, Clyde suddenly seems to gain a new sense of purpose and direction and sets off to meet Sarah Jane and Luke back at Bannerman Road. where he threatens to kill them, while Mr Smith stands idly and insists that "nothing is happening". Clyde's hand glows with lethal energy and he points it at Sarah Jane, declaring that she must be destroyed.

Clyde threatens Sarah Jane but they manage to talk him out of it, which leads Sarah Jane to believe that Trueman's control on people can be repressed by persuading them to do something that they do not normally want to do. Meanwhile, using in his broadcast to the world, Trueman takes over each star sign one by one, starting with Gemini - including Rani's mother, Gita. The world is in confusion as people are accepting the "Ancient Lights". Sarah Jane and her companions head to the New Theatre in East Acton to stop the broadcast, but the possessed Children of Gemini threaten to stop them. Clyde bluffs his way through by making up horoscopes.

The Ancient Lights create a portal through to the theatre. Trueman reveals that Luke's theory on the Ancient Lights is true. Trueman insinuates that in the old universe, they used to control all lifeforms. The Ancient Lights survived the Big Bang and needed Trueman to rule the world because, he was the "Chosen One". Sarah Jane tries to talk him out of it but to no avail. Rani and Luke try to shut down the broadcast by flicking the mains switch off, but it is protected by the Ancient Lights' energy. Rani is an Aries and eventually becomes possessed, leaving only people with the star sign of Taurus, which includes Sarah Jane and Clyde, not under Trueman's control. However Luke, who was not born and so does not have a star-sign, realises he can stop the power of the Ancient Lights by breaking Trueman's circle. Realising that he has been beaten, Trueman cannot bear to return to his former life and instead chooses to become one with the stars, disappearing in a trail of golden dust. In the aftermath, the unaware Earth authorities begin a search for Trueman, and Sarah Jane declares the date will be Luke's equivalent to a birthday.

"Part One" features a flashback of David Tennant as the Tenth Doctor using previously broadcast clips from "School Reunion" and "Journey's End". Sarah Jane mentions that she knows "what it's like to be taken over". Previously, she had been possessed in Planet of the Spiders, The Masque of Mandragora and The Hand of Fear. The idea of godlike entities from the universe before our own, deriving their powers from alien laws of physics which no longer apply, is a nod to Virgin Publishing's Doctor Who New Adventures range, for which scriptwriter Gareth Roberts wrote three novels. The Draconians are mentioned in "Part One". They featured in the Doctor Who story Frontier in Space. Clyde mentions Luke nearly bringing the moon crashing down on Earth in The Lost Boy. Sarah Jane speculates that Martin uses a biodamper, a device first seen in The Runaway Bride.