Warning: this review contains spoilers. If you haven't seen the episode, it's best avoided.

Doctor who fans - or "whovians", as they call themselves - were given a real treat on a Saturday night, with Steven Moffat showcasing a blend of great writing skills, a simmering plot buildup and the most drama we've seen since David Tennant's regeneration scene, as 'Dark Water' kicked off the two-part finale for this series.

Danny Pink is supposedly dead within the first five minutes of the episode, kicking off the high octane drama. However, in true Doctor Who fashion, there's nothing to worry about: we have a TARDIS. The unforgettable words of "time can be rewritten" are used against the Doctor from a dejected Clara Oswald, desperate to get Danny Pink back from the dead and the Doctor eventually agrees - after arguably Peter Capaldi's best scene yet on the edge of a live volcano, evoking memories of The Fires of Pompeii. The Doctor and Clara whisk themselves off to the very end - Hell; or the Nethersphere.

The Doctor Tries to reason with a grief- stricken Clara
The Underworld: The Visual Effects team did a great job in designing this one

On their arrival in the afterlife, the Doctor came face-to-face with the mysterious 'Missy' - a character that has raised much discussion this series, mainly about 'who' exactly she is. Missy has been storing skeletons in watery graves, and as the Doctor races through the corridors of the Nethersphere he remarks: 'I feel I am missing something'. The audience are more in tune with the Doctor's continuity than he is; a playful nod at how the re-boot of the series has come into public consumption more than ever. If the BBC production team hadn't given it away already, the clues were there: emotion edited out, harvesting bodies, etc. Of course the skeletons were not what they seemed; instead, the Doctor’s old silver foil foes, the Cybermen. Revealed not to be the after-life but actually St. Paul’s cathedral, the Cybermen marched down its steps to to delete mankind - a satisfying nod to the iconic 1968 scene in which they did the very same.

Iconic : The 1968 scene was given a satisfying appraisal

Moffat gave his usual mix of playful scenes and serious moments, but it was the latter that touched. Danny had an affecting flashback to the Afghan war - and came face-to-face in the Nethersphere with the very child that he killed while on duty in the army. There was something dark about Moffat's themes: the idea that the dead are still conscious - bringing to the fore the awfulness of cremation - is heavy stuff, and the Danny/young child dynamic brought about several lump-in-the-throat moments. It wasn't all doom and gloom, however, as the show weaved in its light-hearted elements: a kiss that left the Doctor reeling and Clara smirking; and a laugh-out-loud scene where the Doctor tries to warn mankind but is declared to be 'just another ranting Scotsman'.

Danny Remembers life as a soldier

The sucker punch came at an eventful climaxx. Even though the audience has figured it out say fifteen minutes earlier, the Doctor was still playing catch-up with Missy's unmasking. Somewhat inevitably perhaps, she turned out to be a Timelord - or Timelady, now maybe; another interesting nod at the shows ability to switch and change and grow with the times. Despite being expected, there was a bit of clever wordplay on Moffat's part: Missy was indeed 'short for Mistress - well, I couldn't very well be calling myself the Master, could I?' Missy/Mistress/The Master. Simple, but effective. Yes, the Doctor's nemesis from Gallifrey was back from the grave. Capaldi staggered backwards in shock, looking more haunted and grey than ever.

The Doctor finally finds out 'Missy's' identity

So what has Moffat got in store for us in the final part? Could the Master and The Doctor finally resolve their differences? Will Clara bring Danny back from the dead? and can the new-look Cybermen be stopped? One thing is for sure: it promises to be a lively affair.

We'll find out on Saturday Nvember 8. 8:15pm, airing on BBC one. You certainly won't want to miss this one.