The story sets up a mildly antagonistic relationship between the various incarnations of the Doctor, for humorous effect. The Second and Third Doctors bicker, compete, and try to put each other down. Even the First Doctor dismisses the others by saying, "So you're my replacements - a dandy and a clown!" This kind of relationship between the Doctor's selves was seen again in subsequent multi-Doctor stories. Patrick Troughton and Jon Pertwee in particular enjoyed the banter so much that they carried on the mock competition whenever they appeared together at science fiction conventions.
William Hartnell's scenes were filmed at BBC's Ealing Studios and not in a garage or a garden shed as fan myth would have it. However, due to Hartnell's failing health, the promotional photographs were taken at Hartnell's home in Kent. First in the back garden, and then in the garage. This would be the only time that all three actors would appear together.
Frazer Hines was supposed to return as Jamie McCrimmon, and he would have had a romantic subplot with Jo. However, Hines was busy with Emmerdale Farm (1972), and his lines were given to Sergeant Benton. There were also talks of Wendy Padbury returning as Zoe Heriot, but Jon Pertwee vetoed it, as he felt that too many returning characters would be distracting.