The concluding part of Paul Cornell's brilliant double-hander more than delivered on the promise of last week. Where the first half had mystery, the second had drama. Indeed possibly the most dramatic episode of Doctor Who I've ever seen, it had conflict, romance, pathos, hope, fear, courage, fortitude and, in the end, retribution and recognition. A most fulfilling and well-rounded end to a finely crafted story that has raised the bar for the rest of the writing team and given us fans a far deeper insight into both the man and the Time Lord.

Taking her courage in both hands, Martha managed to grab Mother-of-mine (aka Jenny)'s gun and turn the tables on the Family. She ordered the others to clear the room and forced the rest of the Family to back down. Unfortunately, while she was backing out, a scarecrow soldier relieved her of the weapon and she only just managed to escape.

Back at the school, the Doctor ordered the boys to break out the guns and begin defending the building. The rumpus woke the headmaster who was unconvinced by the Doctor's tale of killings and mayhem until Joan backed his story up. Martha's opinions were, as usual, ignored, so she set off in search of the watch.

Sister-of-mine was instructed to infiltrate the school while father-of-mine was sent to investigate why Martha was regularly seen walking West, and eventually discovered the Doctor's TARDIS. Meanwhile the pompous headmaster was given a lesson in war by Baines (aka son-of-mine, etc) which culminated in his deputy being vapourised, thus removing any doubt in his mind regarding the Doctor's version of events.

Martha appeared to be unable to convince Joan of the truth about the Doctor but later, when they were alone, Joan quizzed him about his early (fictional) life in Nottingham and soon realised that something about his story didn't ring true. Inside the school sister-of-mine found Tim Latimer, who recognised her as one of the Family and defended himself with the watch, thereby revealing its presence, and significance, to the whole Family. Baines ordered the scarecrows to attack and the boys did a grand job of defending themselves with rifles and a gatling gun, much to the Doctor's consternation. And mine. But I wasn't worried about the moral implications of young boys using automatic weapons. I was more concerned with why animated sacks of straw would be affected by machine-gun fire.

I soon recovered from my only sceptical moment of the evening when the headmaster tried to remove sister-of-mine from the line of fire and was vapourised for his trouble. So much for chivalry. The Family entered the school and began to search each of the boys, looking for the watch. The Doctor and Joan, with Martha in tow, sought sanctuary in the old farm house - now abandoned after the family had been possessed by the Family. Having failed to call the Doctor out to reclaim his TARDIS, they fired up their armaments and began to bombard the village.

The Doctor, as John Smith, suffered a crisis of confidence, which was exacerbated when Tim (finally!) turned up to hand over the watch. John Smith wanted to carry on being John Smith. To be human and live a normal human life. In an achingly poignant series of flashforwards, John closed his hand over Joan's with the watch sandwiched between them, and they saw their lives play out: marriage, children, grandchildren and finally John's death at a ripe old age, safe in his own bed. Meanwhile, folk in the village were dying and it was time to make a decision.

In the Family's ship, the guns were still blazing when John Smith arrived to plead with them to take the watch and leave him to his normal life. Only, of course, it was a trick. Baines grabbed the watch and opened it to discover...there was nothing left of the Doctor in it. Because the Doctor was back in the Doctor and while he'd been staggering around pleading for his "normal life" he'd been accidentally bumping up against exactly the right combination of levers and switches to set the Family ship onto a self-destruct sequence.

In the ensuing explosion, the Doctor was able to overcome the Family and give them their dearest wish: to live longer. Only it wasn't quite in the way they were expecting. Father-of-mine was tied in chains forged from Dwarf Star Alloy, mother-of-mine was thrown into the event horizon of a collapsing galaxy, sister-of-mine was trapped inside a mirror and Baines, as the narrator of their fates, was immobilised and forced to stand in a field, in a scarecrow costume. As he said: "we wanted to live forever, so the Doctor made sure that we did."

The Doctor gave the now empty fob watch to Tim, who took it off to war where it told him when the time had come that he had foreseen while it still held the Doctor's essence, and enabled him to dodge an incoming mortar and survive. The Doctor and Martha paid Tim one last visit: at a WWI memorial service when Tim was over a hundred years old.

This excellent yarn was the watershed episode, or episodes, of the series for me. While some, many even, of the previous stories have been good (most notably the first one), this was simply outstanding. We learnt more about the Doctor, both as a man and as a Time Lord, than we ever knew before. The story was strong, the acting was in parts exceptional and the character of Martha, which has been criticised by some, finally came into her own and was able to show us what she's made of. Hats off to David Tennant though. Completely believable as both John Smith and the Doctor, and totally different in character from one moment to the next. I really hope the rumours of his leaving part way through next series prove untrue. I would love to see him beat the record for the longest Doctor in history.

Off topic: For anyone in the Manchester area I can thoroughly recommend the "Doctor Who - Up Close" special exhibition at the Museum of Science and Industry which runs until November 5. The Empress of the Racnoss is almost as impressive face to face as she was in the Runaway Bride.

Next week: Blink.