The plot of Heaven Sent works because the Doctor works out the clues from the previous loop.

How did he work out that everything would reset at the end of the first loop without any clues from a previous loop? What did he do in the first loop to set up the second (and subsequent) loops?

  • 1
    If this is the episode I'm thinking of, I think the Doctor merely survived the first loop.
    – Martha
    Nov 16, 2017 at 23:18
  • @Martha If he merely survives, he does nothing to set up the next loop, unless he's able to do everything by coincidence.
    – CJ Dennis
    Nov 16, 2017 at 23:19
  • 2
    He didn't survive it so much as he ensured a second loop. He had to die to do that. The only thing we know for certain is that he died to power the machine to create another copy, like all the others. I don't think anything else can be said about the first loop.
    – J Doe
    Nov 16, 2017 at 23:21

4 Answers 4


In the first loop, he came up with the solution.

In all the loops, including the first one, he determines where he is. The clues about that are all there from the start. Also the knowledge that the rooms reset, which is what he uses to come up with the plan on copying himself using the teleporter. So in the first loop, he determines he's in his Confessional Dial, figures out that he can use the teleporter to keep recycling himself, and that, with that ability, the only way out is through the wall. The only thing that would be different between the first and subsequent cycles is the knowledge that he had been there before.


Spoilers all around, you have been warned!

This episode has a bit of a problem concerning how the loop starts.

Remember that each room resets to its original state when the doctor leaves it. It is a crucial plot point. (Since it is necessary to start the loop.)

One hypothesis (on which I am still uncertain) can really change the way you see it, so I'm going to list both sides:

1. The castle was crystal clear when The Doctor first came inside it

In this case, the first loop start is ... edgy at best: how does the inscription written by The Doctor stay? How do the skulls stay? How does the shovel appear in the hallway? Why does the reset allow these elements to stay in place?

The only way to allow it would be that the resets of the "initial states" of the rooms can be changed by The Doctor dying (his skull does remain in place). Or that the small objects are not affected (why ?)

In this case, The Doctor, while dying the first time, thought of this solution to try again, with maybe small differences, and the loop converged on the loop we are seeing.

This explanation is a bit ... "try-to-make-things-worky" for my taste.

2. The loop is part of the hell

The castle is pretty much a purgatory for The Doctor. Since, at the end of the loop, he remembers all of the others, the loop can be seen as part of the hell. A reason to make him give up. It also has the advantage of always keeping him alive (since killing him is not the point).

In this version: the loop was designed as well as the castle.

My preference goes for the second explanation. But I have no in universe reason to favor one over the other.

  • Considering the dramatism shown in the end of the episode, I'm convinced that author of the script would like us to think about how hellish it is, knowing and remembering each loop and so forth for billions years. But it's clear that Doctor learns everything from the start every time, doesn't he? Even if he realizes or remembers everything just before being stabbed, that's a lot less of torment just understanding this, compared to living through this continuously. Nov 17, 2017 at 10:10
  • 1
    He remembers when he realise that his escape is (or is supposed to be) beyond his reach)and at this moment, the creature appears, leaving him with the escape of confessing to avoir having to restart the loop in a 2 days long agony (the time to reach the tower). So that's pretty horrific, especially when you have been doing that for several millions years. The fact that this is a realisation, the weight of knowing that he cannot escape and that he will be trapped like this again is supposed to crush him. Knowing all along would not have this weight.
    – Edelk
    Nov 17, 2017 at 10:13
  • Clearly, the entire castle doesn't reset -- the Doctor keeps cycling between the two coats, for instance. But he still has to figure it all out the first time through, or at least that he'll go through it again so he can leave himself clues.
    – Zeiss Ikon
    Nov 17, 2017 at 13:43

Nothing changed between loops except the passage of time and the hole he was slowly, punch by punch, making. The Doctor "teleports" in, roams around, chased by the mysterious figure, comes to the end, and realizes he's been chased to this point to force him to make the big confession. Faced with that, or trying to find a way through the crystal but dying in the process, he chooses the latter. It takes billions of years but each iteration makes progress until he escapes.

The only thing the first iteration (or probably even the first few hundred) would have had differently is the inability to know if the punching would work or not. It was equally as likely that the crystal would reset, just like the other rooms. Had it reset, the Doctor would have truly been trapped.


There are a few possible explanations, but one important note is that the rooms don't reset with each new loop (that is, each time he activates the transport device), but rather they reset when he leaves/reenters that specific room. So that means the only things that would be different between the first and subsequent loops are:

  • The state of the crystal barrier.
  • The location of stars and galaxies.
  • (Presumably) the number of skulls in the water.
  • The writing in the ash/sand in the teleport room (this only persists because he doesn't technically leave the room between the loops).

Basically, even the first time through, the entire state of the prison is set so that he'll figure things out and activate the next loop. As to why this is the case, we're not quite sure. What we do know is that the prison was especially designed for him, and that it was made by the Time Lords. This leads to several possible options:

  • The device knew his personality well enough to know what to place where. The dial is essentially a personal hell, designed to torture him specifically to get the desired confession. It could predict his behavior down to the finest detail because it knew everything there was to know about him. This seems well within the grasp of Time Lord technology.
  • Speaking of Time Lord technology, how do we even know there was a first loop? Doctor Who doesn't seem to have any problems with causality loops, or even temporal paradoxes, except when that's the focus of the episode. We've seen that a Tardis can be turned into a paradox-maintenance engine (S3 finale?), so it stands to reason that the Time Lord prison could maintain a temporal loop that didn't have an actual start. Wibbly-Wobbly, Timey-Wimey and all that...
  • Maybe things were actually quite different the first time, but remember the only real difference is the word "bird" scrawled out in the teleport room. Maybe he went through the rooms in a different order or confessed different things based on what he was thinking the first time through, though ultimately coming to the same conclusion and trying to leave himself a hint for next time. Perhaps he left different clues the first few times ("dig", "tunnel", "confess" etc. might have seemed like useful clues the first time through), but "bird" was the first one that worked in such a way that he figured things out and decided it was good enough to leave for the next loop as well. Essentially, an unstable system, that may have worked totally different the first few times through, eventually converged on a stable loop.

While ultimately we just don't know, hopefully this has provided some food for thought.

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