10 Doctor Who Plot Holes You Didn't Realise Were Actually Solved

10. Why Doesn't The Wall Reset In Heaven Sent?

Steven Moffat has always had a knack for intricately-constructed stories that play with time travel, with episodes like The Girl in the Fireplace, Blink, and The Big Bang all garnering huge acclaim.

His timey-wimiest though has to be Heaven Sent, where the Doctor is trapped and endlessly reliving the same experiences for billions of years. It’s such an interesting and well-executed premise that it’s really no surprise that it was immediately recognised as an all-time classic upon its release.

And yet for such a tightly-wound script, there’s one large detail fans have pondered over since broadcast: if everything in the Confession Dial constantly resets, how is the Doctor able to (very slowly) punch his way through the diamond wall? Shouldn’t it reset too, along with everything else?

The answer, it turns out, is a rather straightforward one. As Moffat himself points out in an interview, the diamond wall isn’t inside the confession dial at all; it’s the exterior wall. It doesn’t reset because it’s the container inside which the resetting happens.

This also gives an indication as to why the Time Lords considered a metres-thick wall of solid diamond a reasonable investment. If they want the Doctor to remain trapped inside their torture dimension you might as well make its walls out of something he could never break through.

After all, who’d be crazy enough to spend infinite lifetimes punching diamonds with their bare hands?