Most satisfying villain defeat?

{Spoiler}Waters of Mars' titular watery foe serves as an antagonizing force, but functions more like a force of nature than a proper villain. Which is fitting, because also central to this story is the idea of "history" as this kind of inexorable, immutable force. An exquisite tapestry where tragedies are woven into triumphs, and even forgotten horrors contribute to the whole. For much of the episode, time itself plays the villain, as it is the "foe" seeking the deaths of all these wonderful people we've just met.

And then comes the finale.

Turns out the Doctor was the villain all along, it's just that neither he nor we could see it. (Not quite as uncommon an even as one might initially assume.) I've certainly expressed... misgivings with how the story handled Adelaide's death in the past. But now I see it as making a perfect sort of sense that she, ultimately, is the one with the agency -- it's her choice whether or not to return to her family and live out the rest of her days in relative peace, or opt out in an attempt (that may or may not work) to restore a timeline she knows only the bare minimum about.

That her decision is suicide speaks volumes of the 10th Doctor's cruelty here. She may not know it, but Adelaide is here, on Mars, because of him. But the Doctor knows. And what is it that convinces Adelaide that it is ultimately better for her to die? Certainly not anything the Doctor actually said, or even did -- rather, she is persuaded (to my mind) by his demeanor. (An unlikely observation from someone like me, I'll concede.)

Through him, Adelaide sees the power of her own death. Not just her own story, but the stories inspired by her story. An endless cascade of rippling futures spread in out across the stars.

Only she has to die for it to happen.

So how is this villainous Time Lord defeated, in the very hour of his victory? By way of epiphany. The moment the gunshot rings out, he knows. He put Adelaide on Mars, he arrived in time to see her brutally killed by a fantastical monster, he gave her both the awareness of her fate and the hope that she might escape it, and finally he succeeded in saving her -- and only her -- while also informing her of everything her survival would cost.

And you can see it in his eyes, in that moment. He knows. All of it is his doing. And that added guilt is just one straw too many, and he breaks under the weight of his own martyr complex. In this one scene, we see the Doctor realize that it's time for his own story to end.

Queue up The End of Time.