"Did we come to the end of the universe because of a nursery rhyme?"

Clara asks the Doctor to explain their latest adventure pretty late in the game, and it takes us this long to realize that this may not be the normal sort of mission for the duo. The episode begins with the Doctor pacing and speaking to himself, becoming unnerved at the idea of perfect hunters and creatures that could have evolved to be perfectly hidden. He decides to go on a hunt for just such a creature, but this is the rare episode that sidetracks that goal relatively quickly.

Warning: Massive spoilers ahead

Which is part of what makes this episode so interesting, even including some plot threads that are left completely hanging. This version of the Doctor is driven by the need to understand and to improve, but he's also the most alien of the recent Doctors.

This is the lens through which we have to view this season: What does it look like when something that isn't a man, something that has had nearly unlimited time and opportunity to explore, decides to try become a better, more moral individual? How monstrous could that journey become?

This isn't a story that begins because of external action, this is an example of the Doctor going hunting for something he believes exists. It also shows the power of Clara having a life outside of the TARDIS, as the story mixes with her attempts to go on a "normal" date to great affect.

This hour of television shows an immortal being trying to learn more about a nightmare from his past, but it also deals with someone trying to make the best of an awkward situation. The fact that both aspects of the episode are given equal weight is delightful, and serves to show just how hard it is to juggle a "normal" life with being one of the Doctor's companions.

"Listen" is an episode of Doctor Who that will be discussed for quite some time, and every bit of it works. The stakes are huge for the characters, even if the main plot becomes something of a snipe hunt, but both the Doctor and Clara grow and learn about who they are and what they're trying to do with themselves.

We also see, and begin to understand, the power that Clara wields due to her connection with the Doctor. In one hour of television she changes the course of multiple lives, not to mention the role she plays in guiding and changing the identity and basic personality of the Doctor himself from an early age.

Every bit of it works

She gives a young child the idea of becoming a soldier while trying to comfort him, and the importance of that action echoes throughout his entire timeline. While the specifics of Clara's relationship to Danny and Orson Pink is never fully explained, she's now become an important part of who they are and where they're going.

The use of the toy soldier throughout the episode is an interesting visual metaphor for the Doctor, but more importantly it underscores an important part of Clara's character: As a teacher, and through her gifts in dealing with young children, she's impacting the future. She gets to do so directly in her travels with the Doctor, but every teacher does this on some level by touching the growing minds of the children in their care. Every interaction we have with a child is a ripple we send through our own timelines, for good or ill.

This is what makes the final scene so affecting and brilliant: The Doctor has many gifts, and is an overwhelming presence in the life of anyone he touches. This is something the show has explored, and wrestled with, throughout the years. But in this one interaction Clara meets him when he's a small boy, scared of the dark, and she instinctively knows how to give him strength and help prepare him for what's coming in his life.

She has a way with children, and seeing her use it in this way goes a long way towards strengthening her character and impact on the story.

This is a tense, unsettling episode that moves a few of the larger pieces of this season around in ways that are immensely and immediately satisfying. By the end of the hour we still haven't learned what was under the sheet, but it could have been anything, or nothing. For all we know it was another child.

We've also been given some interesting background on the Doctor himself. We now know that becoming a Time Lord is a thing you do, not something into which your born. We know he wanted to become a soldier, which changes how we see his interactions with other soldiers earlier in this season. These are big, big additions to the character, although it has been hinted at before.

This is an exploration of fear and growth, and "Listen" goes a long way in cementing Capaldi's immediate near-mastery of the character.