"The Time of Angels" is a two-part episode of Doctor Who, released in 2010 and featuring The 11th Doctor, and his companion, Amy Pond, as well as mysterious archaeologist River Song. It was written by Steven Moffat, The second episode is "Flesh and Bone", but as usual, I will treat them as a single story.
The story was significant for several reasons. It was the first two-part story that featured the team of Steven Moffat as head writer and Matt Smith as the 11th Doctor. After four years of David Tennant's portrayal of the 10th Doctor, with the head writing done by Russel T. Davies, many fans were skeptical that those years could be topped. And this was one of the episodes that quickly dispelled that skepticism. It delivered with a cosmic and scary storyline, moments of charisma, and hints to even deeper mysteries.
SPOILERS!
But I am getting ahead of myself: the story brings back the Weeping Angels from "Blink". Whereas "Blink" had been a bottle episode set in 21st century earth, this brings back the Weeping Angels as a cosmic horror in a space opera setting. In the 51st century, a space liner carrying a lone Weeping Angel has crashed, and River Song, a mysterious archaeologist with an unexplained connection to the Doctor, has called on him for help. River, the Doctor, Amy and a team of clerics explore the memorial cave where the lone, weak Weeping Angel is hiding amongst inert memorial statues. And then, they realize that the cave isn't full of memorial statues: it is full of dormant weeping angels that are slowly reviving due to energy escaping from the crashed space liner. Weeping Angels are indestructible and vicious, with their only weakness being their inability to move while being directly observed. The episode then follows the frenetic escape of The Doctor and his accomplices from hundreds of the Weeping Angels, accompanied by even more cosmic weirdness and plot twists, as well as hints that something even more odd is going on. And the climax of the story is a truly great one, for reasons that need its own paragraph.
The Doctor should always conclude a story by showing either his moral fiber or his superior intelligence. In the second case, the writer has a problem: The Doctor's superior intelligence can't be a matter of technobabble. He can't announce at the last moment that he has reversed the polarity of the neutron flow. It has to be something ingenious, but it also has to be something that depends on sheer wits, and not his technical skill. Something that a careful viewer could have anticipated. And this is the case in the climax here, where The Doctor defeats the Weeping Angels by taking account of a factor that is mentioned several times, and that is very obvious in hindsight.
Along with The Weeping Angels, we see other important things here: Matt Smith shows that as The 11th Doctor he will be both more goofy and more militant than we have seen for a while, we see the developing relationships between The Doctor, Amy Pond and River Song, and we get some more timey-wimeyness. All in all, this episode shows that as much as has been done in Doctor Who, there are still new milestones to be reached.