"Knock, Knock" has the makings of a really great, really delightful Doctor Who Earth-bound adventure. There is a very House Hunters-y opening — only without the obnoxious people who can never seem to grasp the concept of how paint works. There is also a creepy, old house with a spooky landlord straight out of Scooby Doo. And lastly, it features the Doctor (Peter Capaldi) acting like an overbearing parent who couldn't handle his child moving away to college. And then, like every family picnic ever, it is ruined by the arrival of bugs.

Now, these aren't just any bugs, they are giant alien lice that are preserving the body of Creepy Landlord's mother, all because he is unable or unwilling to let her die. People are being swallowed up and devoured by the bugs/house in order to keep a woman alive as a weird, backward version of Pinocchio. Honestly, if that's the price we have to pay for even some semblance of immortality, I do not want it. Just let me go into that good night — when I'm like, 98 or so.

Doctor Who's Steven Moffat answers our burning questions about "Thin Ice"

All joking aside, while "Knock, Knock" doesn't quite have the same narrative potency of last week's "Thin Ice," the climax of the hour still manages to touch on topics of particular relevancy for Doctor Who, which is that of death and grief. And there has been a lot of both in the Doctor's very long life, something that's been well established but something Bill (Pearl Mackie) only learned of last week.

Here, the elderly Creepy Landlord has been crippled by the thought of losing his mother since he was a young boy, and so he doesn't care how she remains alive — or at what cost. By the time he's reached adulthood and later old age, he is well past caring about the effects of his actions as long as it means his own mother remains alive. Every 20 years he preys upon poor college students looking for cheap housing, and after they are gone, he doesn't even have the decency to donate their belongings to Goodwill! He just leaves them to mold and rot in the basement. Very rude, sir.

<em>Doctor Who</em>Doctor Who


Ultimately, the story here is one that is achingly familiar to Doctor Who, and it more or less boils down to the idea that one life is not more important than another, that the preservation of one person's life doesn't outweigh the lives of many. In last week's "Thin Ice," the Doctor poignantly addressed this in his speech about the young orphan boy's life being no less valuable than the man who was born into wealth and comfort, and that's again true here. Eliza is not more important than Bill or her friends in the grand scheme of human existence, and she is able to understand this better than her son. To Creepy Landlord she is everything, just as our own parents are everything to us but faceless nobodies to strangers. That doesn't make them less deserving of life, but it also certainly doesn't make them more deserving either.

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The death of one's parents is of course a sad but natural part of life, and no matter the age when it happens — when we're young or when we're older — the process will never be an easy one. Given what we know about Bill, who lost her mother and was raised in the foster system, this parental theme is likely going to be something that continues to pop up throughout the season, because this isn't exactly something you just get over. The first thing Bill does when moving into her new bedroom is show off the space to a framed photograph of her mother, and then hang it on the wall next to her bed.

The parental theme didn't end with Creepy Landlord or Bill, though. The Doctor's arc involves him refusing to leave Bill in a house that he suspects is more sinister than not. It is the show's version of dropping the children off at college and refusing to go home, only in this case the Doctor isn't so much unwilling to let Bill spread her wings as much as he knows there is something fishy going on and he can't help himself. It's in his nature to answer puzzles and solve problems. He protects people, it's just what he does. Still, it's fun to watch Bill and the Doctor attempt to navigate the situation.

We've previously seen companions who have lives outside of the TARDIS. Amy (Karen Gillan) and Rory (Arthur Darvill) didn't travel with the Doctor constantly during their years with him, and Clara (Jenna Coleman) was a school teacher who had relationships outside of her own travels with the Doctor. However, the Doctor was still intricately tied to Amy and Rory and was also the center of Clara's world. Although it's still early in the season, it seems fairly clear that the Doctor does not and will not share that same space in Bill's life. As she notes, this is the part of her world that the Doctor isn't meant to be in, and it's refreshing to see a companion who wants that bit of separation. Even if she is also equally willing to accept the TARDIS as a free moving truck.

Peter Capaldi is leaving Doctor Who

The episode closes with us once again returning to the mysterious vault, and we're getting closer and closer to discovering its mysterious contents. After last week ended with someone knocking on the vault door, this week we learn that whomever is inside now has a piano to pass the time, and the Doctor is bringing them food, noting that they're both prisoners stuck in this unpleasant situation so they might as well hang out.

I think most viewers assume its the Master (or Missy) who's inside — who else would be so joyous at learning there was a house eating young adults? — but is that too obvious? Maybe next week we'll finally find out.

Doctor Who airs Saturdays at 9/8c on BBC America.