Theory:Doctor Who television discontinuity and plot holes/Horror of Fang Rock


 * Would a time/space machine as advanced as the TARDIS, fitted with sensors and tracking equipment which allow it to traverse the whole universe, really be susceptible to getting 'lost in the fog'?
 * The Doctor is just being flippant. He doesn't want to admit he's steered it wrong again.
 * Also, worth remembering that the TARDIS is notoriously unreliable. It's not hard to believe that those "sensors and tracking equipment" would, in fact, be easily confused by local atmospheric effects.


 * The Doctor and Leela leave quite abruptly at the end of the story, without taking into account the potential danger to vessels related to an unattended, non-functional lighthouse. The least the Doctor could have done was go back and turn the switch back on.
 * Given the nature of the explosion he'd just triggered, it's doubtful any vessels within sight of the blast would have to worry about not seeing land for a while.
 * Also, given what's just happened, it is highly unlikely that particular lighthouse is still going to be functional.
 * We also don't know exactly what time it is when the story ends. It is possible that it was (or at least was intended to be) just before dawn.
 * Furthermore, not switching the lamp on may summon the authorities quicker; those on shore will be alerted that the light has gone out, whereas if they switched the light back on people might think that all was well when it clearly isn't.


 * On departing Fang Rock at the end of the story, the Doctor seems rather upbeat and cheerful for leaving behind a lighthouse full of dead innocent humans, having failed to save any of them besides Leela.
 * Saving millions of lives is something to be cheerful about.
 * Also, he's not that upbeat and cheerful. He's not exactly singing and dancing. The story, after all, concludes with him quoting a gloomy and macabre poem about a trio of lighthouse keepers who vanished into thin air. Just because he's not crying and rending his garments doesn't mean he's in an egregiously good mood about things.


 * The Rutan is strangely lacking in curiosity regarding the Doctor's extra-terrestrial knowledge - he has no way of knowing he is an alien himself. Wouldn't it be inclined to think that maybe it had underestimated the knowledge possessed by the human race, and thus the potential threat they might pose when they attempt to invade?
 * Whatever conclusions the Rutan drew based upon the Doctor's knowledge, it didn't have time to act on them or even to really follow up in questions with him.


 * The Doctor's plan to destroy the Rutan mother-ship at the end of the story hinges on his assumption that it will lower its energy shield to 'conserve power'. Surely when landing on an alien planet about which they know very little, besides that one of their scout ships has already been caused to crash on it for some reason, they would be even less likely to lower their shield than usual. There's economic energy use and then there's just foolhardiness!
 * There's also standard operating procedure, which would guide their actions unless they had reason to behave differently. Given Earth's relative lack of technology, the ship has no reason to think they would need the shield up.
 * Perhaps running an energy shield inside an atmosphere consumes huge amounts of power. So it would be logical for the ship to power it down when landing.
 * The information sent back by the scout would have given the mothership confidence that there was no possibility of the native technology posing any meaningful threat to them, so defensive shields would have been low priority for power use (though one would think heat shields would be very useful on atmospheric entry, but perhaps the shielding on Rutan ships lacks multi-purpose capabilities).


 * It requires an even greater suspension of disbelief than usual for the series that the Doctor can turn a primitive lighthouse lamp, albeit a powerful one, into a weapon destructive enough to down an advanced spacecraft, using only a small diamond.
 * A laser is, after all, just a concentrated light beam.
 * The Fourth Doctor often carries miscellaneous tech and components in his pockets. We can probably assume that he cobbled together the carbon oscillator out of more than just the diamond and the lamp.


 * I wonder just how the events of this story affected the area around Fang Rock. Surely the authorities would have investigated the matter when the lighthouse failed to respond to telegraph signals. No doubt they sent a boat out and found a lighthouse full of dead bodies, with a gaping hole in the side of the lamp room...
 * And so discovered an unsolvable mystery just like Flannen Island. The Doctor knows this, but there's nothing he can do to prevent the authorities discovering a door ajar, an untouched meal, and an over-toppled chair...