One night, a blazing light from the heavens strikes a small-time shyster named Martin Trueman. Within weeks, Trueman has risen to fame for his uncanny astrological ability: seeing into the past and predicting the future. When Sarah Jane attends one of his demonstrations, she's unnerved by the extent to which he is able to divine her history with the Doctor. But when she confronts Trueman about the source of his abilities, he becomes hostile, warning her against interfering with the power of the Ancient Lights. Although Sarah Jane is unbowed, she is unaware that Trueman's malign influence already extends to one of her friends.

Gareth Roberts was a key contributor to the first season of The Sarah Jane Adventures -- writing Revenge Of The Slitheen and Whatever Happened To Sarah Jane? -- and he remained heavily involved in the programme as it moved into its second year. Roberts and lead writer Phil Ford collaborated on the development of Gita and Haresh, the parents of new main character Rani Chandra. As such, Roberts' first story for the 2008 season was initially intended to put a strong focus on the Chandra family. He began working on a serial about astrology, which would function as a sequel to one of Sarah Jane's adventures with the Doctor: 1976's The Masque Of Mandragora. Written by Louis Marks, it had introduced an alien energy force called the Mandragora Helix which possessed an astrologer and tried to pervert the dawning of the Renaissance. Roberts' idea was that, with half a millennium having passed, the Mandragora Helix would have now come back into alignment with the Earth, but its agent this time would be a down-on-his-luck swindler posing as a fortune teller.

Roberts was working on his scripts in late 2007. At this point, it was Luke who was possessed by the “Great Star” -- that is, the Mandragora Helix. Clyde, on the other hand, was resistant due to his utter contempt for astrology. Martin Trueman's assistant was originally called Adriana rather than Cheryl. In the climax to the first episode, Trueman was confronted on television by a skeptic named Professor Steven Gordon, who ultimately became possessed. Sarah Jane, too, fell under the influence of the Helix for a time, before she was able to reject it and convince Trueman to do likewise. This act foiled the Helix's plans, and the end of the conjunction meant that it would have to wait another five hundred years to try again. Trueman survived the experience, and he was taken into custody by the Unified Intelligence Taskforce (UNIT).

The production team was unhappy with links to The Masque Of Mandragora

During the development of what became Secrets Of The Stars, however, the production team became unhappy with the links to The Masque Of Mandragora. It was felt that the original serial's threat had to be altered and watered down too much to suit the needs of The Sarah Jane Adventures. Instead, it was agreed that the entity controlling Trueman should be an original creation: the Ancient Lights.

Because production of the season's first story, The Last Sontaran, had to be deferred until June to accommodate the availability of departing star Yasmin Paige, Secrets Of The Stars was brought forward to be made alongside the second story, The Day Of The Clown, as part of the year's initial recording block. Director Michael Kerrigan focussed on The Day Of The Clown at the outset. Early work on Secrets Of The Stars was restricted to inserts and material in Sarah Jane's attic -- filmed at the programme's regular studio space at Upper Boat on April 14th and 16th -- and an establishing shot of Bannerman Road, which was captured at Clinton Road in Penarth on the 18th. A more substantial amount of material was completed at Clinton Road on the 25th.

On April 28th, work began at Cardiff's New Theatre, which posed as the East Acton New Theatre, before shifting to nearby Crockherbtown Lane for the alleyway sequences. May 1st saw cast and crew return to Clinton Road. From May 6th to 8th, the venue for Trueman's stage act and broadcast was actually the Parc & Dare Theatre in Treorchy. Then it was back to the New Theatre on May 12th, for scenes in Trueman's dressing room and outside the theatre. On the 13th and 14th, the Fostering and Adoption Resource Centre in Penarth provided space suitable for Trueman's apartment. A final day at the Parc & Dare Theatre followed on May 15th.

From that point, all of the outstanding sequences were confined to the studio. May 16th saw two teams at work -- one at BBC Broadcasting House in Cardiff for the various newsreaders, and the other at Upper Boat on the sets for Sarah Jane's attic and the Chandra residence. Further sequences on the same Upper Boat sets were then filmed on the 19th and 20th. Production on the story concluded with a variety of inserts, which were taped at Upper Boat on June 27th. This was Kerrigan's final work on a Doctor Who-related project, and he retired from television soon afterwards.

• Doctor Who Magazine Special Edition #23, 24th December 2009, “Episodes 2.5/2.6: Secrets Of The Stars” by Andrew Pixley, Panini Publishing Ltd.