With the Doctor once again free to wander in time and space, the TARDIS brings him and Jo to a cargo ship. The Doctor believes it is the 1920s, until he learns that the boat is one which history records as having disappeared without a trace. It soon becomes clear that they are in fact trapped within an outlawed Miniscope, which holds prisoner a menagerie of oblivious creatures from across time and space.

Having delivered the first adventures for both Season Seven and Season Eight -- Spearhead From Space and Terror Of The Autons, respectively -- Robert Holmes was once again commissioned to pen a storyline for Doctor Who on May 6th, 1971. Entitled “The Labyrinth”, the proposed serial was constructed with the limitations of the Doctor Who budget very much in mind: Holmes split the action evenly between two locations with distinct guest casts, meaning that only half the actors would have to be hired for each of the two studio recording blocks.

The four scripts for “The Labyrinth” were commissioned on November 24th; soon thereafter, the serial was retitled “Peepshow”. In consultation with script editor Terrance Dicks, Holmes had added the subplot about the attempted overthrow of the Inter Minoran president; Dicks was concerned that otherwise the only real threat facing Vorg and Shirna was the penalty for breaking the planet's importation policies. Inter Minor itself was named Odron for a time (with the world hosting a convention of showmen). Pletrac was originally called Pletrac 4, while Kalik and Orum were earlier named X10 and Grig 07, respectively. The unseen President Zarb was referred to as X8, while earlier drafts saw the Miniscope called the Strobe and then the Glo-Sphere. The name Drashig, meanwhile, was an anagram of “dish rag”.

Early in 1972, Dicks and producer Barry Letts began to firm up plans for Doctor Who's milestone tenth season. It appeared likely that several serials for the new year would incur significant costs. Consequently, the inexpensive “Peepshow” was a natural addition to the schedule to help balance the books, and the story was placed second in the running order.

One of the anniversary serials, The Three Doctors, would see a reunion of all three actors to have played the Doctor -- Jon Pertwee, Patrick Troughton and William Hartnell. With Troughton's schedule uncertain, it was decided that “Peepshow” would be made at the end of the ninth recording block to give the production team more flexibility when it came to taping the multi-Doctor adventure. The practise of recording a story for the next season alongside those for the current year had been commonplace on Doctor Who in the Sixties, but had so far been abandoned during Pertwee's tenure on the programme. “Peepshow” therefore became Serial PPP. Pertwee was booked for all twenty-six episodes of Season Ten on February 9th, with Katy Manning's contract extended for at least twenty-two episodes the next day.

As “Peepshow” neared production, Dicks elected to draw upon some of Vorg's dialogue to retitle the adventure Carnival Of Monsters, although Holmes preferred the previous moniker. Letts, meanwhile, had decided to direct Serial PPP himself; a clause in his contract permitted him to direct one story per year, the previous instance being Terror Of The Autons. As John Andrews, Letts cast actor Ian Marter, who had been offered the role of Mike Yates in 1970 but was forced to withdraw his name because he could not make an ongoing commitment to the series.

Location filming got under way on May 30th at Tillingham Marshes in Essex for scenes in the Drashig environment. Part of the next day was also spent at Tillingham before cast and crew relocated to the Carwoods Quarry in Asheldham, Essex for material at the cave mouth. On June 1st and 2nd, the team boarded the RFA Robert Dundas at Chatham, Kent; the ship, which was soon to be decommissioned, posed as the SS Bernice. Production there was interrupted when it was discovered an old brass ship's compass had been stolen. The culprit turned out to be none other than Pertwee himself, who believed that the compass was to be scrapped along with the Robert Dundas and so wouldn't be missed (in fact, it was to be auctioned off along with other ship artifacts).

Production then moved to the studio beginning on June 19th; recording days were Mondays and Tuesdays, as they had been for the rest of the production block except for the previous serial, The Time Monster. The 19th and 20th were used for all the scenes taking place aboard the SS Bernice and inside the Miniscope workings. July 3rd and 4th were then spent on material set on Inter Minor and in the Drashig cave; unusually, neither Pertwee nor Katy Manning were needed for the Monday. Unfortunately, toward the end of the second day, the headpiece Peter Halliday wore as Pletrac began to detach from the actor's scalp, as could clearly be seen in the scene in which Vorg demonstrates the Magun Pod Concession game.

Carnival Of Monsters experienced a number of edits in postproduction for timing reasons, most notably the excision of the original cliffhanger to part three. This would have seen the Doctor falling down a shaft when a Drashig comes upon him in the Scope interior. In the episode four reprise, the Drashig plummets after him and the Doctor is seen to have been saved by catching his foot in a rope. As broadcast, this sequence was skipped over altogether, and the Doctor's emergence from the Miniscope -- originally to have occurred during episode four -- was brought forward to serve as the cliffhanger instead.

Another late change was to the theme music used for the story. Letts had commissioned a new version of Ron Grainer's original composition from the BBC Radiophonic Workshop -- the first wholesale rearrangement since Delia Derbyshire's original work in 1963. The new, more electronic-sounding, version was performed by Paddy Kingsland on a synthesizer dubbed the Delaware (due to the Workshop being situated on Delaware Road). Unfortunately, the so-called “Delaware theme” met with resistance from Letts' superiors, and so although it had already been dubbed onto Carnival Of Monsters, it was subsequently replaced by the more familiar arrangement. Nonetheless, an early edit of episode two, complete with the Delaware theme, was inadvertently shipped to Australia.

• Doctor Who: The Handbook: The Third Doctor by David J Howe and Stephen James Walker (1996), Virgin Publishing, ISBN 0 426 20486 7.
• Doctor Who: The Seventies by David J Howe, Mark Stammers and Stephen James Walker (1994), Virgin Publishing, ISBN 1 85227 444 1.
• Doctor Who Magazine Winter Special 1994, “Archive: Carnival Of Monsters” by Andrew Pixley, Marvel Comics UK Ltd.
• Doctor Who Magazine Special Edition #2, 5th September 2002, “Saturday Night's Alright For Fighting” by Andrew Pixley, Panini Publishing Ltd.