The final episode of the season, the final episode (give or take one) featuring Peter Capaldi's Doctor, seemingly the final episode of The Master - in two of his incarnations, no less - and the final episode (more or less) of showrunner Steven Moffat.

That means there's a lot to say in a short space of time. And a lot of ground to cover.

What lies ahead is a Moffat-penned Christmas episode but as a weekly adventure in space and time, this season finale carries Moffat's signature in a way that few other episodes do.

There is no doubt that Moffat, who replaced the rebooted show's first showrunner Russell T. Davies, has put his stamp on the BBC's most valuable programming asset Doctor Who.

His art is one of blending humour, darkness and pathos with touches of affectionate nostalgia; his exhumation of the Ice Warriors, glimpses of the robotic Movellans and even a cameo from the "hermaphrodite hexapod" Alpha Centauri have made the series sparkle.

The season finale, The Doctor Falls, is easily the equal of Moffat's best writing across the series: the riveting 50th anniversary special The Day of the Doctor, the edge-of-your-seat-terrifying Blink and heart-crushing love story of The Girl in the Fireplace.

The premise, as with all of his best episodes, is breathtakingly simple: a small, low-tech community led by Hazran (Samantha Spiro) struggling to fend off attacks from scarecrows who are, essentially, prototypes of the low-tech Cybermen encountered by William Hartnell's First Doctor back in 1966's The Tenth Planet.

This clash becomes something of a last stand, an injured Doctor fending off an army of Cybermen and his impending regeneration - that is, the body-healing evolution that has cranked a dozen or so actors through the role since 1963 - by the sheer force of his will.

As Hazran, Spiro was dazzling. Think of her as a sort of Laura Ingalls Wilder with laser guns. And if you don't know Spiro's work, find it. Her Birgit to Tracey Ullman's Angela Merkel in Tracey Ullman's Showis hilarious and her evocation of Barbara Windsor in Cor, Blimey! and Babs is breathtaking.

At its heart, the episode explores one of the most powerful but rarely acknowledged themes in Doctor Who: the price paid by the Doctor's human companions who have been as significant a part of the show since its inception as Daleks, Cybermen and (other) Time Lords.

Russell Davies stabbed into the topic in his epic Dalek finale Journey's End, when Davros - the crippled scientist who created the evil Daleks - said of The Doctor accusingly: "The man who abhors violence, never carrying a gun, but this is the truth Doctor: you take ordinary people and you fashion them into weapons."

"How many have died in your name?" Davros asked Tennant's Tenth Doctor, describing his nemesis as "the man who keeps running, never looking back, because he dare not, out of shame."

In the tenth season finale too, the price is hefty: The Doctor's companion Bill Potts (Pearl Mackie) turned into a Cyberman.

Here she is beautifully (and tragically) juxtaposed by an alternating visual dance between Bill as she imagines herself (that is, human) and the brutal reality of the bandaged, dehumanised creature she has become.

To some extent there is a creative necessity in that; the "Mondasian" Cybermen (as they are known in Doctor Who lore) have mechanical voices which alternate in pitch and, frankly, sound silly, even in 1966. The episode's director Rachel Talalay had to find a way and did a brilliant job of it.

Such personal relationships should not be the sin of a Time Lord, the ancient, decaying civilisation at the apex of cosmic history whose silent stewardship of space and time had, for all intents and purposes, withered to haughty indifference.

It's the reason the Fourth Doctor (Tom Baker) unceremoniously dumped Sarah Jane Smith (Elisabeth Sladen) in a suburban London street "without so much as a bye or leave".

And the reason why, when Sarah Jane re-encountered The Doctor in his David Tennant incarnation, she demanded he say goodbye properly.

This is also the first story in which two incarnations of The Master are present, played by John Simm and Michelle Gomez, a stark contrast to multi-Doctor stories, of which there seems to be an overabundance.

Story note for Doctor Who newbies: Time Lords "regenerate" through 13 "incarnations". Simms's Master followed Roger Delgado, Anthony Ainley and others, and regenerated into Gomez's Missy, just as Hartnell's First Doctor has lived through a succession of lives, notably played by Jon Pertwee, Tom Baker, David Tennant and, now, Peter Capaldi.

While multi-Doctor stories usually were marked by bickering between the different Doctors, Simm and Gomez relished in the opportunity here to play through their relationship in a variety of ways: two skewed halves of one brain, or the narcissist (Simm) sexually attracted to the sociopath (Gomez).

The relationship truly flourishes, however, as their differences begin to manifest themselves. Simm's Master is truly unredeemable, a proper heir to the Roger Delgado incarnation, who clashed with Pertwee's Third Doctor back in the 1970s.

But Gomez also taps a rarely explored aspect first evidenced in Delgado's Master, that as Time Lords, ultimately, The Master and The Doctor had much in common. Gomez's Missy has brushed with being more of an ally than an enemy, and here she hopes to takes the full step.

"Winning? Is that what you think it's about?" Capaldi's Doctor asked the two Masters as the end approaches. "I'm not trying to win. I'm not doing this because I want to beat someone. Or because I hate someone. Or because I want to blame someone.

"It's not because its fun," he added. "God knows it's not because it's easy. It's not even because it works because it hardly ever does. I do what I do because it's right. Becase it's decent. And above all it's kind. It's just that. Just kind."

Moffat saves the best for last, however, and in the episode's final moments Capaldi's Doctor staggers out of his time machine, and encounters the First Doctor, played here by David Bradley. (Hartnell died in 1975.)

Like a last lick of the plate, we are treated to a succession of references to past episodes: Tennant's last words "I don't want to go", Baker's flashback of companions calling out to him, the Tardis cloister bell (a warning of imminent disaster), and, finally, the encounter with his original incarnation.

"The Doctor? Oh, I don't think so, no, dear me, no," the First Doctor says. "You may be a Doctor, but I am the Doctor. The original, you might say."