The TARDIS lands on a planet which will explode in mere hours. The Doctor, Vicki and Steven discover that two alien species -- the beautiful Drahvins and the hideous Rills -- have crashlanded on the planet after a battle in space. The Doctor races against the clock to determine which of the aliens are their foes and which their friends, before the destruction of the planet annihilates them all.

Around the time that Dennis Spooner became Doctor Who's story editor at the end of October 1964, one of the writers due to meet with the Doctor Who production team was William Emms. Emms had gotten his start as a writer of short fiction before moving on to television, including programmes such as Z Cars and Private Eye. Emms was eventually commissioned to script “The Chumblies” on March 1st, 1965. Ironically, it would be in development just as Spooner was preparing to depart Doctor Who, to be replaced by Donald Tosh.

“The Chumblies” was originally written for the companion team of Vicki, Ian and Barbara, causing problems when Emms had to replace the latter two with Steven. Steven largely assumed Barbara's role, meaning that he would sometimes behave in an uncharacteristic manner, including letting the Drahvins (initially called “Dravians”) trap him in an airlock, despite his astronaut origins. Another change to “The Chumblies” was suggested by producer Verity Lambert, who recommended that the Drahvins all be female.

The story, designated Serial T and renamed Galaxy 4, went into production in June 1965, around which time John Wiles had largely replaced Lambert as Doctor Who's producer. The director allocated to Galaxy 4 was Mervyn Pinfield. Pinfield had served as the programme's associate producer during its first year or so, and had recently directed The Space Museum. It was planned that Galaxy 4 and the succeeding one-episode serial, Mission To The Unknown, would basically be made as though they formed a single, five-episode serial concluding the second recording block, with the same crew handling both.

Five days of filming began at the Ealing Television Film Studios on June 22nd, with sequences needed for both Galaxy 4 -- chiefly material on the planet's surface -- and Mission To The Unknown planned for these dates. At this stage, the name of the Drahvin leader was changed from “Gar” to “Maaga”. Unfortunately, as work progressed, Pinfield fell badly ill and it became clear that he was in no condition to continue. At the time, Derek Martinus was a candidate to direct The Myth Makers, the opening serial of the third production block, and he accepted Lambert's request to substitute for the ailing Pinfield on both Galaxy 4 and Mission To The Unknown. Martinus had first been an actor in Britain before travelling to the United States to study directing. He worked in both Canada and Rhodesia before finally being accepted into the BBC's internal directors' training course. Doctor Who would be his first work as a BBC staff director.

Martinus took over the Ealing schedule on June 24th, albeit with Pinfield's advice until the end of filming. Meanwhile, trouble was brewing behind the scenes for the new production team of Wiles and Tosh. None of the stars liked Emms' scripts, and things became so heated that Wiles even threatened to fire William Hartnell at one point.

With Martinus now in sole control of the director's chair, recording started at BBC Television Centre on July 9th; each installment would be recorded on consecutive Fridays as usual, with the first three episodes taped in TC4 and the last in TC3. Unusually, it was decided that the final scene of The Exploding Planet -- the cliffhanger into Mission To The Unknown -- would be recorded as part of that serial's single recording day on August 6th, to avoid having to erect an extra set and hire actor Barry Jackson (playing Garvey) a week early. On July 30th, the final day of production on Galaxy 4, Maureen O'Brien received a revised version of her contract. This included a BBC option for 20 further episodes beyond The Myth Makers.

The end of taping on Galaxy 4 also marked the last day of work on Doctor Who for Hartnell, O'Brien and Peter Purves for more than a month. Because Mission To The Unknown was designed to feature none of the regular cast, they would not be reunited in the studio until the start of the third production block in September. Galaxy 4, meanwhile, was held over to start Doctor Who's third season, beginning on September 11th.

On October 14th, Wiles inquired with the BBC Copyright Department about ownership of rights to the Drahvins, suggesting he had plans for a return appearance by them, although this did not transpire. Galaxy 4 was also William Emms' lone Doctor Who work. A second story, “The Imps”, was planned for Season Four but never made. Emms would later use elements of this adventure for a 1986 Doctor Who novel entitled Mission To Venus, which formed part of the Find Your Fate range. Other proposed Doctor Who storylines submitted by Emms included “The Harvesters” for the Second Doctor around 1969, and “The Zeldan” and “The SCI”, both written for the Fifth Doctor in about 1983. He also novelised Galaxy 4 for WH Allen in 1985. Emms wrote for a plethora of television programmes both in the UK and Australia -- such as The Newcomers, Ace Of Wands and Crossroads -- before leaving the industry in 1989. Emms had begun a career as a novelist when he died in 1993.

• 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 #299, 10th January 2001, “Archive: The Time Meddler” by Andrew Pixley, Panini Publishing Ltd.
• Doctor Who Magazine Special Edition #7, 12th May 2004, “The Times They Are A-Changin'” by Andrew Pixley, Panini Publishing Ltd.