Note: Doctor Who TV’s pre-air reviews aim to be as detail-free as we reasonably can while still offering a critique, but as everyone’s spoiler sensibilities are different, we advise you read on at your own discretion.

Heaven Sent presents a big dilemma for a pre-air review, more so than usual. There’s an awful lot to talk about, but there’s also an awful lot that shouldn’t, rather experienced first hand. Really it’s in your best interests to just see this one and soak it all up. Several times. Over and over for millions of years…

Following on directly from the events of Face the Raven, we pick up immediately with the Doctor teleported to a very strange place. He appears to be trapped in a mysterious castle that can change form at certain moments. And he’s not quite alone either. Someone or something is watching, and a strange creature, the Veil, is stalking him at every turn.

One of Doctor Who’s best features as a show is its flexible format. One week you can have a tried and tested base under siege story and the next something completely different, something that completely turns the established formula on its head. Granted, not all experimental episodes completely pay off (see Love & Monsters, or this year’s Sleep No More), but it’s worth the gamble when you get a complete success story like Heaven Sent.

Yes, this is a very special story in more ways than one. It’s Moffat’s best episode in this reviewer’s opinion since The Day of the Doctor. If you took Listen’s opening sequence (Capaldi talking to himself), and extended it into 50ish minutes you have a rough idea of what to expect.

At the same time though, for as loved as Listen is, that does it a bit of a discredit. Heaven Sent goes several steps further. It’s deeper, you need to watch it several times to appreciate and it’s completely absorbing. Full of metaphors and open to interpretation, people will get many different things out of it. Some may dislike it for its shunning of a conventional format and strangeness, but for those that it clicks with, it is utterly rewarding.

If you thought Capaldi was good in The Zygon Inversion that was just an appetiser. Sustaining a 50-plus minute episode pretty much by yourself is no mean feat, but Capaldi is more than up to the task. If there’s any justice in the world, awards will be thrown at him for the range and depth of his performance here. We see the Doctor pushed to his absolute limits. It’s also quite distressing at times with the Time Lord physically and mentally tortured with very visible wounds (the Daily Mail will have a field day!).

Clara may be gone, but she’s certainly not forgotten. She lays heavy on the Doctor’s mind for a large part of the plot. As the trailer and promo pics show, the castle cruelly reminds of the loss he has endured at several turns. It’s a dark and bleak episode, which at times seems like all hope is lost. But there is a glimmer at the end of the tunnel.

As previously mentioned, there is a monster of sorts, but like the episode itself the Veil isn’t your traditional variety. It never speaks, you never learn much about it, but that doesn’t make it any less effective. In fact it’s the other way round – what you don’t see is far scarier.

Returning Director Rachel Talalay deserves large recognition for putting this complex episode together. For a story that is essentially just one (mad) man trapped in a castle, it’s to her credit you never feel bored. There is a constant visually changing landscape with the palette varying from old school horror to the more psychological. Also deserving praise is Murray Gold who has to score more of the episode than usual, with some haunting melodies to keep fans on their toes.

The long-teased cliffhanger isn’t quite as shocking or surprising as made out to be, but the journey leading up to it is the most intriguing part. It’s a very special episode and one that will hopefully be treasured by the fanbase. More like this please, Steven!