Theory:Doctor Who television discontinuity and plot holes/The Edge of Destruction


 * The Doctor tells Ian that they only have 5 minutes to survive in episode 2 - yet it takes over 5 minutes before they release the fast return switch. The Doctor even takes time to deliver a long and rather pointless speech when he knows that their end is only a few seconds away.
 * Time has since been shown to pass differently inside the TARDIS. As for the Doctor becoming extremely excited about a scientific phenomenon, that is completely consistent with his character, as we have since seen.
 * The five-minute (or worse) estimation of their survival seems to be a conclusion the Doctor has reached from the system-wide failure on the fault locator (implying that the whole ship is on the verge of disintegration). It later turns out that this fault signal was merely one of the TARDIS's increasingly desperate attempts to communicate with the travelers (therefore not actually indicating the ship was already falling to bits around them, but hinting that it could very well do so if they kept on ignoring a certain jammed switch ...).
 * Furthermore, once he and the rest of the crew pin the fault down to the Fast Return Switch, they move to fix it as fast as they can. Before this, though, he and Ian both believe the TARDIS to be doomed. The Doctor fairly explicitly indicates to Ian that they're all going to die, and that the two of them should simply try to appear busy, making progress, talking- giving Susan and Barbara false hope so that they won't despair, and will receive an instantaneous and unknowing merciful death, rather than cowering waiting for the end.  During the long, rambling speech, the Doctor is probably still expecting to be annihilated at any second- but, how would he prefer Susan to die? Watching her grandfather excitedly revelling in a scientific phenomenon and with hope and confidence that any moment he'll find a way to use it to save them, or in terror and despair, waiting hopelessly for an inevitable end?


 * William Hartnell, completely throwing the other actors during one scene by saying the same line ("It's not very likely") twice, and fumbling "You knocked both Susan and I unconscious". He also omits the scripted explanation for the melted clocks.
 * The Doctor, like many people, sometimes stumbles over his words.
 * The line he repeats is actually "It's not very logical" and Jacqueline Hill gives the scripted response to it the second time around - the Doctor may just be provoking Barbara with the word "logical" until she calls him on it.


 * The fast return switch should have sent them back to 100,000 BC as that was the last place it visited prior to Skaro and not 1963 London.
 * The Doctor was shown to have frequent lapses in memory at this point in his life.


 * Although various later (non-television) stories have claimed the fast return switch returns the TARDIS to its previous location, this is pure fan lore. The Doctor's explanation of the switch here is simply that it sends the TARDIS back in time.
 * How do we know that he hasn't pressed the switch twice, as in later stories such as in Seasons of Fear, to return back to a previous destination he tells Charlie to press the fast return switch three times, which takes the TARDIS back from the Time Vortex to Roman Britain.


 * Since the spring was broken, the TARDIS could have been continuously going back in its history. Much like repeatedly hitting the back button on the browser.  If the TARDIS history is pre-initialized with '0' for the time before the first location, then the TARDIS would head towards the Beginning of Time.  Fixing the problem before reaching that would just land the TARDIS at some location the TARDIS had been to before.  In this case it just happened to end up at one of the times the TARDIS landed in 1963 London before Skaro.


 * If the Fast Return Switch can take them back to previous destinations, why don't they try to use it again? Even if they were worried it might get stuck again they could just check it.
 * Perhaps they did, and found it in the same wretched condition as the rest of the 1960s-era TARDIS control system. In retrospect, it seems that the Third Doctor's enforced exile was the best thing that could have happened to the TARDIS, as it resulted in the extensive dry-dock overhaul it was sorely in need of.