Firstly, how the story panned out . . .
John Smith, the human manifestation of The Doctor hiding in a village in Edwardian England, and Martha are being pursued by the malevolent Family Of Blood, a murderous race who want the essence of a Time Lord to extend their lives.
Martha is desperately trying to convince a confused Smith that the time-and-space-travelling adventurer of his subconscious, The Doctor, is his true form, and she needs him to return to defeat The Family - but she needs to find the stolen fob watch which contains his life patterns.
The boy who stole the watch, Tim Latimer, brings it to them in a deserted house, and even Smith's girlfriend, the matron, Joan, believes Martha to be speaking the truth. Smith is faced with the personal dilemma of opening the watch, in the knowledge that he would most likely cease to exist. He decides to make that sacrifice, and The Doctor destroys The Family's spaceship and gives them the immortality they crave - in a form that they can never do any harm to anyone else.
The Doctor asks Joan to travel with him in the TARDIS, but she rejects him as a result of his role in the death of many innocent villagers.
Young Latimer, with the power of foresight given to him by the watch, narrowly escapes death in The Great War, and goes on to live a long life. The Doctor and Martha return to Earth to visit him as an old man before continuing their travels.
Now, that rough outline of the second episode perhaps doesn't sound that special - but there was so much more beneath the surface that made this one of the finest written and acted characterisation pieces in any Doctor Who.
There were so many great scenes. Early in the episode, there was Martha battling to hold off The Family on her own with their laser gun. This was a great story for Martha, with more to do in two episodes than some previous companions had to do in two series! Without "The Doctor" for most of it, she was left to effectively take the lead against a more-advanced race, and had to cope with her own feelings of hurt that her beloved Doctor in his human form had fallen for another woman.
Plenty for Freema Agyeman to get her teeth into, and she didn't fail to deliver. If, as rumours have it, her first series is also to her last, that would be a sad loss to the show. I think both actress and character still have much to offer.
Another extraordinary scene was the scarecrow soldiers' attack on the school, defended by armed pupils. The sight of pre-teenage boys firing rifles at their assailants was a chilling reminder that lads of not much older went off to war in real life in that time period and, in fact, still do today all over the world.
From a filming perspective, it was one of many superbly-realised action scenes overseen by director Charles Palmer, who has made a big impression this season, and we'll hopefully see more of his work in Series 4. It rather reminded me of a brutal scene in the first episode of Genesis Of The Daleks, which saw men in gasmasks being gunned down in a trench, and made a vivid impression on this young man of eight or nine in 1975.
Curiously, although the scarecrows were made of straw, seeing their innards splatter out as they were shot was surprisingly effective. It sounds like a funny scene, though was anything but, and the excellent direction and lighting was a large contributory factor here.
The scary scarecrows themselves worked marvellously well throughout the two parts. From Ailsa Berk's clever "lolloping" choreography to the malevolent tilting of the head to the actual design, they were a triumph. The production team could have got them very wrong, but they were very right.
Also "very right" was John Smith being given a foretaste (via the watch) of what his human life could be like - through marriage and children until death. This was the life The Doctor can never have (and, deep down, doesn't really want as "he could have changed back"). Making David Tennant up as an old man was another great job from Niall Gorton and his prosthetics team, as it was with Mark Gatiss in The Lazarus Experiment.
The closing scene of The Doctor and Martha returning to Earth to visit the elderly Latimer was touching, but perhaps the finest scene of the episode - and maybe the entire series - was The Doctor meeting Joan after despatching The Family.
This was a significant scene because it clearly showed the arrogant side of The Doctor. Having been partly responsible for the devastation which befell this innocent village upon which he descended, he then assumes Joan will be grateful for the opportunity to travel with him in the TARDIS - and without any mention of poor Martha, who has constantly risked her life to save him. Joan's quiet and dignified dismissal of him with a "you can go now" was an even better put-down than Jackie Tyler's slap of the ninth incarnation.
Superb stuff from Jessica Hynes as Joan - I think she would have made a fascinating short-term companion - and David Tennant was absolutely immense here again, in his dual roles as John Smith and The Doctor. And it was the former which was arguably the more likeable of the two in this episode. The portrayal of Smith's struggle to grasp what was going on and then make the decision to give up his life enabled Tennant to underline the range of his ability.
I'm rather inclined to gloss over rather unconvincing elements of the plot, notably The Family's sudden demise. Having The Doctor "just press buttons" on their spaceship to make it blow up was a slight let down, and you could argue that the whole premise of the story was rather elaborate if The Doctor could just revert to Time Lord status, and had the power to confine The Family to "a life sentence" straight away.
That said, I wouldn't be up all night worrying about things like that when there was so much to enjoy. The idea of "giving those who seek immortality what they wish for" was actually explored at the end of The Five Doctors. It's a rather-chilling prospect, and the little girl trapped in the mirror was another intriguing concept.
There was a nice nod for fans with a snatch of Ring O' Roses (as accompanied a similarly-malevolent little girl from Remembrance Of The Daleks) and a reminder that a fanboy runs this show! And is making a pretty fine job of it . . .
This was the best story of David Tennant's tenure as The Doctor for me, and possibly the finest since Caves Of Androzani. Nine and a half out of 10, and surely even the blinkin' majestic Steven Moffat can't top this little gem next week. Can he?