"Let me be brave," whispered a doomed Clara Oswald last week. She could take a tip from BBC One - it requires balls to air one of Doctor Who's most experimental, risky and downright odd episodes to date on a Saturday evening in the wake of gushy glitter-fest Strictly Come Dancing.

'Heaven Sent' is an adventure so deliberately dark and obtuse that it's practically begging for a divided reaction. What's known in 'the industry' as a single-hander, it features no (major) speaking parts other than Peter Capaldi's Time Lord.

But writer Steven Moffat cleverly subverts the expectation that this'll be a low-budget escapade, with a surplus of Capaldi awkwardly expressing his inner thoughts aloud. There's plenty of the Doctor 'talking to himself', true enough, but there's always a reason.

Early on, he's tough-talking the unseen presence that's brought him to this "killer puzzle box" in the middle of a vast ocean. Later, in a series of surreal cutaways he shares imaginary 'conversations' with an absent Clara.

It's this second device that Moffat uses to delve deeper than ever before into our lead's alien thought process, to provide a visual representation of how his mind actually works.

There's the impossibly quick thinking that allows him to escape certain death. His insatiable desire to learn more and uncover answers. And the huge degree to which his companion(s) is responsible for pushing him onward.

But while it's not afraid to be intellectual, 'Heaven Sent' is not just a pondering talkathon. and anyone dreading Doctor Who's answer to Waiting for Godot should find themselves pleasantly surprised.

BBC

Early on, it's a mad and bewildering dash, with a shaken and introspective Doctor trapped in his own personal hell, stalked by a shadowy menace. But this bespoke prison is designed to provoke a confession - the truth will, quite literally, set you free - and it's this conceit which allows Moffat to litter his script with enormous reveals.

That the Doctor left his home planet for reasons other than a thirst for adventure is a game-changer that shakes the show to its very roots. But it also ties into the series arc of the Hybrid in the episode's spectacular final moments. Did our hero flee Gallifrey to save it from himself?

One thing's for certain - even after 5 years in the job, showrunner Moffat is refusing to rest on his laurels, switching up not just the show's style but its substance. He's out to prove that you can still do something new with a character that's been around for half a century.

Fed such strong and intimate material, Capaldi's performance is sensational - frenzied, passionate and haunting. And his 'co-star', the Veil, is genuinely horrific. The scenes in which it stalks the Doctor, its presence heralded by the buzzing of stray flies, is the stuff of nightmares.

'Heaven Sent' is brilliant, but it's also about as far from big, broad, family-friendly entertainment as you can get. The show's been obtuse and a little odd before, but nothing quite like this, and its rejection of the standard Doctor Who trappings might be too much for some.

But if you're willing to see past that and embrace the weirdness, then you'll end up captivated. Because this is demanding and intelligent science-fiction, the likes of which BBC One should be commended for airing in any slot - let alone straight after we've watched Peter Andre dance the American Smooth.

TARDIS Scanner:

- So the Doctor is the Hybrid. Does this mean Moffat's confirming the old 'half-human' notion from the Paul McGann TV movie?

- The Daleks would never allow a half-Dalek hybrid? I presume Steven Moffat has forgotten all about the Human Dalek? Lucky him.

- Gallifrey's back!! But who trapped the Doctor in the castle? Was it the Time Lords? Were they somehow responsible for Clara's death?

- Just to be clear, the Doctor we have now isn't the real Doctor? He's a replica? Or rather a replica of a replica of a replica of a...

- It's rather ironic that for all the Timey-Wimey shenanigans, the Doctor eventually escapes his prison by doing the one thing he never does - using his fists.

- Speaking of violence, there's some properly brutal moments in 'Heaven Sent' - I doubt anyone will be complaining about the late evening slot this week.

- One of the finest moments in that mindbending climax is the realisation that the Doctor's 'fresh' clothes were in fact his own wet clothes, previously discarded, now dry by the fire.

- Should Jenna Coleman's brief cameo have been omitted? It's a nice emotional moment, but it does rather go against the concept of a single-hander.

- Psychic link with a door. PSYCHIC LINK. WITH A DOOR.

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