The story is set in Yuan-era China in the year 1289, where the Doctor (William Hartnell), his granddaughter Susan Foreman (Carole Ann Ford), and her teachers Ian Chesterton (William Russell) and Barbara Wright (Jacqueline Hill) meet the Italian merchant-explorer Marco Polo (Mark Eden) and Mongolian Emperor Kublai Khan (Martin Miller).

Lucarotti—who had previously written works based on Marco Polo's adventures—was suggested to producers by Doctor Who creator Sydney Newman when the show was early in development.

It received generally positive responses from critics and was sold widely overseas, but was erased by the BBC in 1967; the entire serial is missing as a result.

The TARDIS, badly damaged, lands in the Pamir Mountains of the Himalayas in 1289, and the crew are picked up by Marco Polo's (Mark Eden) caravan on its way along the fabled Silk Road to see the Emperor Kublai Khan (Martin Miller).

The story concerns the First Doctor (William Hartnell), his granddaughter Susan Foreman (Carole Ann Ford) and her teachers Ian Chesterton (William Russell) and Barbara Wright (Jacqueline Hill), and their attempts to thwart the machinations of Tegana (Derren Nesbitt), who attempts to sabotage the caravan along its travels through the Pamir Plateau and across the treacherous Gobi Desert, and ultimately to assassinate Kublai Khan in Peking, at the height of his imperial power.

[7] The fifth episode featured an untrained spider monkey, which the cast found difficult to work with; Carole Ann Ford recalled that "it was a nasty little thing peeing all over the place and biting anyone who came near it".

[20] Philip Purser of The Sunday Telegraph noted that Eden impersonated Marco Polo "with sartorial dash", but felt that the main characters were poorly written, describing Barbara as "a persistent drip".

[19] In The Discontinuity Guide (1995), Paul Cornell, Martin Day, and Keith Topping wrote that the story was "wonderful, but a little too loose and unstructured to be the all conquering classic of repute".

[21] In The Television Companion (1998), David J. Howe and Stephen James Walker described the serial as "an amazing tour de force", praising Lucarotti's scripts, dialogue, and characters, Hussein's direction, Newbery's sets, Dare's costumes, Cary's score, and the cast performances.

[22] In a 2008 review, Mark Braxton of Radio Times praised the serial, stating that "the historical landscape was rarely mapped with such poetry and elegance", though he noted inconsistencies in the foreign characters' accents.

[23] In Doctor Who: The Complete History (2016), editor John Ainsworth described the serial as "exotic and arresting", praising the simplicity of the narrative and the exploration of the characters.

A three-CD set of the audio soundtrack was released in November 2003, as part of the show's 40th anniversary, with linking narration by William Russell and a fold-out map of Polo's journey.