Space Security Service agent Marc Cory arrives covertly on Kembel. Cory and his team are on a mission to uncover the plans of the Daleks and their intergalactic allies, who are secretly meeting on the planet. But Kembel is a world of many dangers, and as his companions slowly transmute into deadly Varga plants, Cory soon realises that for him, there is no escape.

In October 1964, Head of Serials Donald Wilson ordered that the opening story of Doctor Who's second season, Planet Of Giants, be trimmed to three episodes from four due to a perceived lack of dramatic impetus. At the time, it was suggested that the Dalek story planned to be made at the end of the second production block (which would later be abandoned and replaced with The Chase) might be expanded from six episodes to seven as compensation. Nothing came of this.

Nonetheless, it was likely because of the loss of the fourth Planet Of Giants episode that, around the start of 1965, Head of Drama Sydney Newman extended the second recording block from twenty-six episodes to thirty-five, rather than a more obvious allotment of thirty-four. By this time, Doctor Who stories were being made exclusively in either four or six parts, and so the addition of nine episodes to the schedule would force a deviation from the usual pattern.

At around the same time, Terry Nation was completing work on The Chase. Keen to repeat the success of the transmission of The Dalek Invasion Of Earth during the Christmas 1964 period, producer Verity Lambert and story editor Dennis Spooner asked Nation to contribute another six-part Dalek story for broadcast around November and December 1965. In tandem with this, it was decided that the extra episode remaining at the end of the recording block could be used for a special “trailer” for this new Dalek adventure. To save on the cost of contracting the regular cast for the additional installment, this would be the first Doctor Who episode to feature neither the Doctor nor any of his companions. Nation was commissioned to write this one-off, given the title “Dalek Cut-Away” and the production code DC, on February 25th.

The popularity of the Daleks by this stage was so great that Nation was beginning to mull the possibility of a Dalek spin-off programme, perhaps even one which could be exported to the United States, a market Doctor Who had so far failed to crack. He therefore viewed “Dalek Cutaway” (as the episode became known) as an opportunity to lay the groundwork for such a show. As such, Nation developed the concept of the Space Security Service (also called the Special Security Service and the Space Special Security Service) and Agent Marc Cory, whom Nation conceived as a “space-age James Bond” (building on the popularity of the Bond movie franchise, recently spiked by the release of Goldfinger). The Service would later feature prominently in The Destroyers, Nation's unmade 1966 pilot script for his proposed Dalek series.

“Dalek Cutaway” was originally set on the planet Varga. Around July, the name was altered to Kemble and then Kembel. The Varga plants themselves retained their original name, but now became artificial creations of the Daleks, brought to Kembel from Skaro, as opposed to a natural, indigenous form of life. The alien delegate Zephon was deleted from the script, presumably due to financial concerns. Also in July, the name Mission To The Unknown was applied to Nation's script although, confusingly, the “Dalek Cutaway” title would also continue to be used in some documentation. (Indeed, some sources suggest that Mission To The Unknown is the title of the single episode which makes up a serial called “Dalek Cutaway”.) Rather than leading into a standard six-part Dalek story, it was by now known that Mission would serve as a prologue for an unprecedented twelve-episode adventure called The Daleks' Master Plan.

Due to its unique nature, it was decided that Mission To The Unknown would be made by the same crew as had been assigned to the previous story in production, Galaxy 4 (Serial T), including director Mervyn Pinfield. Filming at the Ealing Television Film Studios would also be carried out for the two adventures simultaneously. Because of this -- as if the confusion over its title wasn't enough -- Mission would henceforth also be referred to as Serial T/A, Serial Ta, and even “Serial T Episode 5” in addition to the previously-assigned Serial DC.

Although the filming dates assigned to Galaxy 4 and Mission To The Unknown spanned June 22nd to 26th, the brevity of the latter meant that it would only be featured on the schedule for the final day. By this time, Pinfield had fallen badly ill and had to be replaced at short notice by novice director Derek Martinus; Pinfield would retire from television soon afterward, and passed away in the mid-Sixties.

With Martinus at the helm, Mission enjoyed its lone studio session on Friday, August 6th in TC4 at the BBC's Television Centre (a change from the originally-planned TC3). Recording of the episode itself was preceded by the enactment of the final scene of Galaxy 4's concluding installment -- the cliffhanger into Mission -- which had been held back to avoid having to both hire actor Barry Jackson (Garvey) for two weeks and erect the Kembel set an extra time. The completion of Mission also brought Doctor Who's second production block to a close.

By the time Mission To The Unknown was taped, Spooner had already left Doctor Who to be replaced as story editor by Donald Tosh. Lambert, too, had all but handed over the producer's reins to John Wiles, and this would be her final credited serial: a photocall was held on the day of recording to mark the end of her involvement in Doctor Who. Lambert would go on to produce a number of critically- and popularly-acclaimed programmes, including The Newcomers, Adam Adamant Lives! (which, like Doctor Who, was created by Sydney Newman), Quatermass, Minder and Jonathan Creek. She became the Controller of Drama for Thames Television in 1979, and in the Eighties formed her own production company, Cinema Verity. Lambert was awarded the Order of the British Empire in 2002; she passed away following an illness on November 22nd, 2007.

• Doctor Who: The Handbook: The First Doctor by David J Howe, Mark Stammers and Stephen James Walker (1994), Virgin Publishing, ISBN 0 426 20430 1.
• Doctor Who: The Sixties by David J Howe, Mark Stammers and Stephen James Walker (1992), Virgin Publishing, ISBN 1 85227 420 4.
• Doctor Who Magazine #271, 18th November 1998, “Archive: Mission To The Unknown” by Andrew Pixley, Panini UK Ltd.
• Doctor Who Magazine Special Edition #7, 12th May 2004, “I'm Into Something Good” by Andrew Pixley, Panini Publishing Ltd.