Doctor Who - beautiful and appalling!

They called it the beginning of the end for David Tennant but something far more serious has happened in Doctor Who,

.

Don't read this if you haven't seen Waters of Mars yet because it is the end of that episode, which left me dumbstruck and paralysed on my sofa, that I wish to discuss.

In all his travels through space and time the Doctor has lost just three companions. The first two, Sara and Katarina, fell victim to the Daleks in the time of William Hartnell. The other, boy genius Adric, sacrificed himself to destroy the Cybermen in Peter Davison's era. Serious, but noble, ends.

In the second of four specials that mark the death and regeneration of David Tennant's tenth Doctor his companion, played by Lindsay Duncan, was so horrified at the immense power of the Last of the Time Lords to change history that she blew her brains out.

As an adult watching that program with my partner I thought it was one of the most powerfully dark moments I've seen on TV all year. A moral debate will, I'm sure, continue among older fans until Christmas.

I can only speculate as to how parents of young children will have felt. I'm sure that watching the Flood, the water infected zombies of Mars, chasing the cast down corridors into confined spaces was thrilling for all ages. Kids need to be scared from time to time.

But that ending has me concerned. It was both beautiful and appalling all at the same time.

We saw the Doctor riddled with guilt over his inability to act, then fired up by the realisation that he was the only Time Lord, and the laws of time were his to apply.

We saw him snarl as Adelaide questioned his right to impose his will on the history that is yet to happen. If it had ended there I would have been applauding. Finally, here we have a Doctor to be ever so slightly scared of. He's brilliant, he's kind but he's vicious and a cosmic hypocrite, bursting with conflicting emotions that come from years of never being accountable to anyone for his actions.

This must also be Tennant's finest hour in an absolutely outstanding run. As he walked away from the base, hearing the screams through his space helmet he conveyed more emotion through his eyes than all his hyperactive, wide-eyed jigging ever did.

He lurched with an almost bi-polar tendency from enthusiasm and joy to furious self-righteousness it was exhausting to even watch him but addictive at the same time.

I've no doubt about the power of the story telling and acting, Tennant's face wracked with horror over Adelaide's suicide brought about by his actions was a triumph.

This episode should have set us up perfectly for the final two-parter at Christmas, where the Doctor's chickens come home to roost and he is forced to once more submit every single cell of his body to the cosmos as Rassilon's great gift to the Time Lords makes him sacrifice all he knows simply to survive.

But, the children. Won't somebody think of the children? Loathe as I am to admit it usually this is a children's show. Lindsay Duncan's character was advertised to them as a companion. Her name appeared in the opening credits. Her survival after almost insurmountable peril is meant to be as fixed an occurrence as the volcano eruption of Pompei.

Waters of Mars told the children that there are no rules anymore. The companions do not just run off with clones of the Doctor or get their minds wiped. They are now susceptible to taking their own lives.

Was it a step too far for the youngsters? Will it ever be safe to be scared again?