Androvax the Veil returns to Earth, but this time he claims to be seeking Sarah Jane's help. Dying from an incurable poison, Androvax is trying to recover a spaceship which carries the cryogenically-frozen survivors of his doomed planet. The trail has led him to a mysterious vault hidden beneath a disused asylum in London, but it is guarded by androids led by the impassive Mister Dread. With the fate of an entire species at stake, Sarah Jane is forced into an uneasy alliance with one of her most sinister enemies, little realising that Androvax's designs may have terrible consequences for the Earth.

When he was appointed the lead writer of The Sarah Jane Adventures with its second season, Phil Ford became responsible for three out of the year's six stories. With season three, there had been a conscious effort to diversify the show's writing staff. Ford was only intended to provide two serials that year, but issues with the adventure assigned to newcomer Brian Dooley had resulted in Ford overhauling it as Mona Lisa's Revenge and claiming sole writing credit. Likewise, it was initially expected that Ford would write the first and fifth stories for the programme's fourth season in 2010. However, when it was decided that the 2010 episodes would be made alongside the first half of the fifth season, it was agreed that Ford would provide two out of the three serials destined for 2011. As such, only the season premiere was retained of his fourth-season commissions.

A major component of the 2010 season was the departure of Luke Smith from Bannerman Road, with actor Tommy Knight having made the decision to focus on his education. Furthermore, K·9 would be accompanying Luke to university. As such, it was planned that the year's first adventure would serve as a fun, frothy, final romp for the established Bannerman Road gang. Ford began working on an idea in which a teacher at Park Vale Comprehensive was revealed to be an ancient Mayan priestess. This character later evolved into a wealthy woman living in a high rise, who was attempting to open a portal to facilitate an alien invasion of Earth. During the early autumn of 2009, however, Ford found himself struggling with the scripts; he felt that he was just marking time until Luke and K·9's exit, and that this really needed to happen in the opening story. Consequently, Ford's spot in the schedule was swapped with Joseph Lidster, who had been working on an adventure to establish Luke at Oxford University. Both writers would start over again with brand-new storylines, and Ford would now handle the first narrative to take place after Luke and K·9 had moved away.

In UFO lore, the Men in Black were figures in dark suits who tried to silence those who had witnessed alien phenomena

One of Ford's other Doctor Who-related projects had been Dreamland, a six-part animated Tenth Doctor adventure which would be made available in late November via the BBC's Red Button service and the official Doctor Who website. Its storyline made use of various elements of UFO lore which had sprung up -- especially in America -- during the Forties and Fifties. One such element was the Men in Black, figures in dark suits who claimed to be working for the federal government and whose role was to try to silence those who had witnessed alien phenomena. The notion had been used as the basis for a comic book called The Men In Black, created in 1990 by Lowell Cunningham, which was adapted into a popular 1997 film, Men In Black, starring Will Smith and Tommy Lee Jones. In Dreamland, the Men in Black were androids serving an organisation called the Alliance of Shades, which was working to cover up evidence of extraterrestrial activity on Earth. Elements of Dreamland had already made their way into Ford's third-season premiere, Prisoner Of The Judoon.

Ford had enjoyed writing for the Men in Black in Dreamland, and he decided to bring them into The Sarah Jane Adventures. Most notably, he decided to resurrect their leader, Mister Dread, who had seemingly been destroyed by the Doctor in Dreamland, for which he was voiced by Peter Guinness. Ford also developed a shape-shifting alien who would take the form of Rani's mother, Gita Chandra, after locking the genuine article in a potting shed. It was suggested that this role seemed tailor-made for Androvax the Veil, the villain from Prisoner Of The Judoon who could possess human bodies. Ford correspondingly amended his storyline to incorporate Androvax, and he became eager to develop the alien in a new and more sympathetic light.

Ford's story, eventually titled The Vault Of Secrets, was paired with Lidster's serial, The Nightmare Man, to form the initial production block of the 2010 season under director Joss Agnew. The first scene to be recorded for The Vault Of Secrets was Luke's video call, which was taped on the set for his dorm room at the production's usual studio home in Upper Boat on March 30th, 2010. On April 4th, Sarah Jane disabled Mister Dread's vehicle on Ferry Road in Cardiff, while the 6th saw Bannerman Road material taped on Clinton Road in Penarth. Several locations represented the disused St Jude's asylum. The first was Hensol Castle at Hensol, where Agnew shot exteriors on April 7th, as well as scenes in the private ward and the area where the Bannerman Road gang -- and Gill before them -- broke in. The 8th and 9th were spent at St Cadoc's Hospital in Newport for St Jude's sequences including various corridors, the physiotherapy room, and the records room.

After the weekend, more Bannerman Road material was filmed at Clinton Road on April 12th, followed by shots outside Ocean Waters' house on Archer Road in Penarth; work at the latter continued on the 13th. The Men in Black's lair was actually found in the Johnsey Estates, part of the Mamhilad Park Industrial Estate in Pontypool. Work there chiefly spanned April 14th to 16th, although some inserts were also captured on the 19th and 20th. The 22nd was devoted to material in the attic set at Upper Boat. The BURPSS meeting had been scheduled earlier in the block, but it was ultimately deferred to April 29th at All Saints Church Hall in Penarth. The latter part of the day saw Agnew's team return to Upper Boat for sequences in the Chandra residence.

• Doctor Who Magazine Special Edition #28, 13th July 2011, “Episodes 4.3/4.4: The Vault Of Secrets” by Andrew Pixley, Panini Publishing Ltd.
• Doctor Who Magazine Special Edition #32, Autumn 2012, “The Stories That Never Were...” by Andrew Pixley, Panini UK Ltd.