Sarah Jane is summoned by the mysterious Shopkeeper, who warns her that three fragments of chronosteen, a metal forged in the time vortex, have been lost in the Earth's past. Chronosteen has the power to change history, and so the Shopkeeper sends Sarah Jane, Clyde and Rani back in time, each with a mission to recover one of the pieces. Clyde finds himself fighting Nazis along the English coast. Rani becomes caught up in the intrigue of the court of Lady Jane Grey. And Sarah Jane must unearth the secret of a haunted house, and its tragic connection to the future...

Having written The Gift for the third season of The Sarah Jane Adventures, Rupert Laight submitted additional ideas for the fourth season in June 2009. He was asked to develop “The Children Of Blackmere Rise”, a story inspired by the 1975 thriller The Stepford Wives, in which Sarah Jane and her friends investigated a council estate where all of the children seemed abnormally happy. Over multiple drafts, it evolved into a narrative about an alien called Bryce who had been stranded on Earth for centuries, and who was mind-controlling the children in order to calculate the forgotten access code for his ship, which was buried beneath the council estate. Sarah Jane offered Mr Smith's help in exchange for the children's freedom, but this turned out to be a ruse to free Bryce's powerful brother from imprisonment within the ship. In the end, an act of self-sacrifice by Sarah Jane convinced Bryce to turn against his brother.

By October, however, it was felt that “The Children Of Blackmere Rise” was not working out, and Laight met with the production team to discuss a replacement storyline. To this point, The Sarah Jane Adventures had largely eschewed the time travel element which was characteristic of Doctor Who; the only exceptions were two journeys along the lead character's personal timeline in 2007's Whatever Happened To Sarah Jane? and 2008's The Temptation Of Sarah Jane Smith. Some consideration had previously been given to a trip back to the Bannerman Road of the Seventies in an homage to the 1985 movie Back To The Future, but it was now decided that Laight should write a full-throated time travel adventure.

The goal was originally to reassemble the scattered components of a time machine

As his inspiration, Laight looked to Doctor Who's 1978-79 season, in which each of the six serials had formed part of the Doctor's year-long search for the segments which made up the powerful Key To Time. Laight likewise decided that Sarah Jane, Clyde and Rani should embark on a quest which would take each of them to a different point in history, essentially giving each character a mini-adventure of their own. These events would be initiated by a figure called Candleman, and the goal was originally to reassemble the scattered components of his time machine.

Candleman was inspired by the shopkeeper in the 1971-72 animated series Mr Benn, who would send the titular hero back in time through a magic door in the fitting room of his costume shop. However, as the scripts evolved, executive producer Russell T Davies encouraged Laight to keep this character as enigmatic as possible; thus he simply became the Shopkeeper, and the object of the quest was to recover three pieces of chronotite, as chronosteen was originally dubbed. Another of Davies' suggestions was to give the Shopkeeper a parrot to whom he could speak, since the character would often be alone, watching the events which were taking place in the past. Laight christened the bird Captain after the parrot owned by Lady Lavender Southwick in the sitcom You Rang, M'Lord?, which had first aired in 1988.

Each of the three mini-adventures underwent some notable changes during the story's development. Sarah Jane's strand was always set during Victorian times -- a favourite of Laight's -- but it originally dealt with a man who was using the power of an ancient statue to become wealthy by predicting the future. When this notion was replaced by the haunted house, a character called Miss Fuller was retained and became Emily Morris. For the final version, Laight decided to have the ghosts turn out to be emanations from the future, in order to differentiate his story from 2009's The Eternity Trap.

An alternative for Clyde would have placed him at Park Vale Comprehensive in 1973

Laight always intended Clyde to wind up in an English coastal village during the Second World War, but the production team was concerned about this setting and asked him to develop an alternative. It would have placed Clyde at Park Vale Comprehensive in 1973, where he became friends with a group of students who were trying to start a glam rock band. Together they fought an alien who was attempting to recover two pieces of a necklace which gave the wearer control over time. The alien was finally driven away when Clyde's knowledge of the future convinced it that Earth was more technologically sophisticated than it had believed. Ultimately, however, Davies preferred the Second World War version. Laight drew upon the 1942 film Went The Day Well?, and originally included Nazis who masqueraded as British soldiers. Laight also had the vicar, Reverend Bryce, captured alongside Clyde and George, but the character was deemed superfluous. Dialogue eventually cut from the finished serial would have explained that Miss Wyckham had only recently come to Little Malding after the former schoolteacher, Mrs Thwaite, had gone missing.

For Rani's mini-adventure, Laight initially wanted to place her in the court of Anne Boleyn, the second wife of King Henry VIII, who was beheaded in 1536 to facilitate the king's marriage to Jane Seymour, after Anne's failure to produce a male heir. Set during the queen's final days of freedom, this plotline would have included the unmasking of a spy and a scheme to steal a valuable necklace. It was Davies who instead suggested that Rani should meet the ill-fated Lady Jane Grey, the Nine Day Queen who reigned in July 1553. Although he was unfamiliar with the story, Laight ultimately felt that the change was to the betterment of his scripts, since Jane's proximity to Rani's age -- as compared to Anne Boleyn, who was about thirty years old when she died -- helped him root the drama in the relationship between the two characters.

Laight's story was eventually called Lost In Time, and was made as part of the year's third recording block alongside the 2010 season finale, Goodbye, Sarah Jane Smith. It was directed by Joss Agnew, who had recently completed the first two serials, The Nightmare Man and The Vault Of Secrets. Agnew began by concentrating on the 1889 mini-adventure with Sarah Jane. It was filmed at Hensol Castle in Hensol from May 24th to 26th, 2010. Material in Sarah Jane's attic was then taped on the standing set at Upper Boat Studios on the 27th, followed by scenes on the Shopkeeper's premises at Jacob's Market in Cardiff on June 1st and 2nd.

The next plot strand to be recorded was the 1941 sequence involving Clyde. The main focus was St Mary's Church in Bridgend, which posed as St Michael's on June 3rd, 4th, 7th and 8th. Part of the latter day was also spent at Newton Beach in Newton, where the Nazis came ashore. Finally, Rani's escapades in 1553 were filmed at Caerphilly Castle in Caerphilly from June 9th to 11th. The only remaining scene was Rani in her bedroom, which was completed at Upper Boat on the 18th.

• Doctor Who Magazine Special Edition #28, 13th July 2011, “Episodes 4.9/4.10: Lost In Time” 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.