As Saturday night entertainment goes, a profund exploration of grief, fear, suffering and captivity is hardly on a par with pizza and wine. But Heaven Sent wasn't just an all-time classic, with a performance from Peter Capaldi that rivets you to your seat, some of the best direction seen on the series and Steven Moffat's redemption all rolled into one. It was a triumphant return for a show that has frequently lost sight of its own possibilities over the last ten years.
Doctor Who is the only show on television that could do something like Heaven Sent: to command sufficient money and audience attention to get away with it; to play with form and convention as much as it did; to explore the reaches of outer and inner space; dread, loss and despair; moving castles, a sea of skulls and a remorseless wraith. A Grimm fairytale, an MR James short story, a PC puzzle game and a Hollywood blockbuster. It even lifted straight from its own stablemate - the Doctor's mind palace a clear nod to Sherlock.
Doctor Who's magpie tendencies were on full display here - and the show has never felt so confident, so right in its unique ability to do thumb its nose at convention, to write its own script. To go the long way around.
At its most banal these past ten years, Doctor Who has felt like a pastiche of pop-culture references - it hasn't seemed especially different from other programmes and, perhaps, more importantly, from itself. You can draw a straight line between The Shakespeare Code and Root Of Sherwood - or The Lodger and The Caretaker. Modern-day Earth invasion stories and time-travel cats cradles and historical pastiches. Doctor Who has spent a lot of the last decade sending itself up - or serving up warm reheats. But Heaven Sent didn't simply feel like nothing else on television; it felt like no other Doctor Who.
Estates and flat and chips and fleets of flying Daleks and BBC newsreaders and Murray Gold's awful kidult Hollywood music have become a rut for Doctor Who over the last decade: a comfort zone that has become not only a default setting, but a received wisdom: you can't defy the template, they say; you can't put off the casual viewers.
But this sort of thinking is a trap. It forces Doctor Who - that programme of limitless possibilities - into ever-decreasing circles, a room whose walls will only keep closing in. The overall trend of the series has been one of diminishing returns, with adventures into the surreal, uncomfortable or odd - the very things that Doctor Who is known for - more scarce than a two-handed Dapol Davros.
Both of Doctor Who's showrunners have lapsed into these ruts and they are evident in episodes including - but not limited to - New Earth, The Shakespeare Code, Vampires Of Venice, The Poison Sky, Cold War, The Caretaker. Episodes whose only aspiration seems to be to last 45 minutes. Or the patented end-of-series, kitchen-sink gangbangs. Episodes where every last gimmick and lampshade will be deployed to paper over the cracks of a plot that doesn't really make any sense.
Steven Moffat has virtually admitted that his primary motivation when writing Doctor Who is to maintain the attention of people who might be inlined to switch over - an approach that puts me in mind of Magnus Greel having to absorb the life essences of more and more young girls, just to stay alive.
But in supplicating before an audience - serving up the same old tropes, the ones that are familiar and palatable - can never be a sustainable approach. Doctor Who has always succeeded by playing by its own rules, changing, reinventing itself and kicking against expectations. When it's good and daring and different it turns casual viewers into dedicated viewers, into fans. The very people who resurrected the series. How many programmes have the power to do that?
Heaven Sent certainly did. It currently has a 100% rating on Rotten Tomatoes and has been routinely described as one of the best episodes in the show's 52-year history. And it did this in spite of the fact that featured The Doctor alone in an incomprehensible castle, bereft at the death of his friend, in a bespoke torture-chamber. Perhaps because of it. Its audience was good for the slot and Twitter has buzzing for hours afterwards. Heaven Sent was a success by any metric.
It's a modern paradigm that means trying to woo viewers, those viewers who will never like Doctor Who through the modern curse of relatability, is a fool's errand. Russell T Davies' famous aside about the planet Zog is perhaps the most unfortunate observation in modern television and has cast a long shadow over the programme. It's a received wisdom that has closed many doors to the programme and it's based on a whim, a funny soundbite.
The outcome of this is most obvious in David Tennant shouting and Matt Smith waving his arms around and companions fancying the Doctor and Moffat's speechifying and Murray Gold's schmaltz. It's led Doctor Who's makers to only try to make programmes like Doctor Who.
You couldn't have something like Heaven Sent every week. It's a gruelling watch that requires - albeit rewards - attention; it's upsetting, horrifying and slow and features no audience identification figure. Its music is offbeat, weird, dissonant - surely a deliberate echo of the classic show's Radiophonic Workshop synths and it's startling how successful they are in freeing the show of its familiar ambiance. Its direction occasionally reminiscent of Tarkovsky; its chiaroscuro cinematography. A 57-minute one-hander with a 57-year-old lead actor.
All things that have been thought impossible in the modern Doctor Who. No, you couldn't have it every week - but you could have something as different as Heaven Sent every week. It's a story that demands rewatching. Its sheer quality deserves it; as a lesson in what makes Doctor Who vital, it commands it.