Whitaker wrote the scripts in two days, based on an idea he had developed during the show's formative weeks; he sought to explore the characters in more depth, as well as the facets of the TARDIS.

The serial premiered with ten million viewers, maintaining the figures from the previous story, and received generally positive responses.

The First Doctor (William Hartnell), while attempting to correct the TARDIS's faulty navigation circuits, causes a small explosion.

The Doctor, Barbara Wright (Jacqueline Hill), Ian Chesterton (William Russell), and Susan Foreman (Carole Ann Ford) are all temporarily rendered unconscious.

On 16 October 1963, BBC TV's Controller of Programmes Donald Baverstock indicated that Doctor Who was only confirmed as a 13-episode show at the time, due to budgetary information.

Since the serial had no budget and minimal resources, Whitaker took the opportunity to develop an idea conceived during the show's formative weeks: a character-driven story exploring the facets of the TARDIS.

[7] Rehearsals for the first episode began on 13 January 1964,[8] and it was recorded on 17 January in Lime Grove Studios, Studio D.[6] William Hartnell initially complained about the script due to the number of lines, while Carole Ann Ford was sceptical of the characters appearing mad without reason; conversely, Jacqueline Hill and William Russell appreciated the chance to explore their characters in more depth.

[1] In The Discontinuity Guide (1995), Paul Cornell, Martin Day, and Keith Topping wrote that the story "manages to flesh out the central figures at the expense of the plot".

[15] In A Critical History of Doctor Who (1999), John Kenneth Muir praised the serial's exploration of its characters' relationships, an element that the show would eventually lose after the departure of Russell and Hill.

[16] In a 2008 review, Patrick Mulkern of Radio Times described Whitaker as "a master of dialogue, characterisation and atmosphere", but felt he struggled with plot logic, as evidenced by the fast return switch explanation.

[18] The serial was recommended by Charlie Jane Anders of io9 as an example of the classic series for new viewers to watch, describing it as "a quick hit ... and still just as intense as it was".