The TARDIS lands in 1289 China. There it is seized by famed explorer Marco Polo, who intends to present it as a gift to Kublai Khan, in the hope that it will win him his freedom. The Doctor, Susan, Ian and Barbara must accompany Polo as he travels across the desert to the court in Peking, and at the same time unearth the malevolent plotting of Tegana, an agent of a rival warlord whose mission is to assassinate the Khan.

Before moving to Britain, Doctor Who creator Sydney Newman had made a name for himself at the Canadian Broadcasting Corporation. There, he met a writer named John Lucarotti, who had been supplying scripts for CBC Radio since the mid-Fifties including a fifteen-part serial in 1956 about Marco Polo. Lucarotti followed Newman when the latter moved to ABC in England, where he wrote for series such as The Avengers (for which he also declined the post of story editor), Ghost Squad and City Beneath The Sea.

By the time Newman recommended him to Doctor Who story editor David Whitaker, Lucarotti had taken up residence in Majorca, but returned to London in late June 1963 to meet with Whitaker and producer Verity Lambert. Lucarotti was interested in writing an historical adventure for Doctor Who and elected to have the time travellers meet up with Marco Polo, allowing him to make use of the material he had compiled while researching his earlier radio serial. “A Journey To Cathay” was commissioned on July 9th.

In crafting his scripts, Lucarotti drew heavily from Polo's memoirs, published in the fourteenth century as The Description Of The World. The route followed by Marco in the serial was inspired by his first journey to Peking, which culminated around 1275. His escort of Ping-Cho was based on a real event in 1292, in which Marco brought the young Princess Kokachin to Persia to wed a grand-nephew of Kublai Khan only to learn upon their arrival that the older man had passed away. Tegana, Acomat and Noghai were all named for Tartar rulers mentioned in Polo's memoirs. Many of the historical facts included by Lucarotti in his scripts -- such as the descriptions of the Khan's stables -- also came from the memoirs.

“A Journey To Cathay” was originally intended to be the third Doctor Who story. However, in late October, BBC Chief of Programmes Donald Baverstock refused to authorise the series' continuation beyond its initial thirteen-episode run due to budgetary concerns. Since “Journey” was preceded by 100,000 BC (four episodes) and The Daleks (seven episodes), this could have potentially cut the programme off midway through the Marco Polo serial. Therefore, the two-part Inside The Spaceship was commissioned to be made after The Daleks. The production of “A Journey To Cathay”, now the fourth Doctor Who adventure, was finally authorised by Baverstock on November 22nd as part of an order of a second block of thirteen episodes.

The director assigned to Serial D was Waris Hussein. Hussein had previously handled 100,000 BC and it was originally intended that he would alternate serials with Rex Tucker throughout the season. Despite the shifting of “Journey” in the schedule, Hussein remained attached as director, although it was briefly thought that Richard Martin (who helmed episodes of both The Daleks and Inside The Spaceship) would handle the fourth and sixth installments.

By the time five days of filming at the Ealing Television Film Studios began on January 13th, 1964, the serial had been renamed Marco Polo. Various scenes were completed at Ealing, most notably the sword fight in the throne room and those involving significant quantities of water.

Studio recording then got under way at Lime Grove Studio D on January 31st; each episode would be taped there on successive Fridays. William Hartnell fell ill the following week, and so part two, The Singing Sands, was restructured to minimise the Doctor's role. A small error occurred when the “Next Episode” caption used at the end of the installment read “The Cave Of Five Hundred Eyes” even though part four's title had already been abbreviated to simply Five Hundred Eyes.

On February 20th, Doctor Who featured on the cover of the Radio Times programme guide for the first time; the debut episode of 100,000 BC had originally been slated to receive this treatment the previous November. The black-and-white photograph featured Hartnell with guest stars Mark Eden and Derren Nesbitt. Unfortunately, this was to provoke an angry response from William Russell, via his agent T Plunkett Green, who felt that the rest of the regular cast had been slighted by their omission from the cover. Russell was also unhappy with six minutes of new scenes which had been added to episode four, The Wall Of Lies, the day before its recording on February 21st. As a result of this complaint, Lambert granted Russell, Jacqueline Hill and Carole Ann Ford a greater involvement in script appraisal in the future.

Unique of all the episodes of Marco Polo, The Wall Of Lies was directed by John Crockett, a former designer. Crockett was so invigorated by the task that on February 26th he wrote a memo to Whitaker suggesting a number of possible historical storylines Doctor Who might employ. Of these, the Viking raids on Britain, Bonnie Prince Charlie, the Crusades, Catherine de Medici, and Cornish smugglers would all be pursued in some form or another (though Crockett's influence on most of these is doubtful).

On March 20th, Lambert was informed that her request to shift Doctor Who's timeslot back by fifteen minutes, to 5.30pm, had been granted. This would take effect with the sixth episode of Marco Polo, Mighty Kublai Khan, on March 28th. The recording of this episode on March 6th had been preceded with a remount of the closing scene of part five. Taping on the lengthy story finally wrapped up on March 13th.

Despite the original intention that he should direct half the serials of Season One, Marco Polo would prove to be Waris Hussein's final contribution to Doctor Who. His request that he be allowed to concentrate on directing television plays was granted; later, Hussein helmed episodes of programmes such as The Newcomers. He went on to direct the original A Passage To India for the BBC before going freelance in the Seventies. He has since accumulated a large resume of work directing films and TV movies on both sides of the Atlantic, including projects with such luminaries as Bette Davis and Sir Laurence Olivier. Hussein's American commitments prevented him from accepting an offer to direct the Doctor Who twentieth-anniversary story The Five Doctors in 1983.

• 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 #240, 3rd July 1996, “Archive: Marco Polo” by Andrew Pixley, Panini UK Ltd.
• Doctor Who Magazine Special Edition #7, 12th May 2004, “Do You Want To Know A Secret?” by Andrew Pixley, Panini Publishing Ltd.