Tonight the Doctor (Peter Capaldi) is back on BBC America, with what I would venture to say is the best episode so far of the season, "Knock Knock," written by Mike Bartlett and directed by Bill Anderson.

The fourth episode brings back the creepy factor when Bill (Pearl Mackie) looks for a place to live with some friends. After not much success on the hunt, when an old man (David Suchet) shows up offering them a place that seems too good to be true, they jump to sign the contract from the landlord. But when they hear creaks in the walls, it may be more than just an old house, as her friends start disappearing.

The first three episodes this season had a variety of light and dark moments, but "Knock Knock" was what I was waiting to see, one a bit more scary.

The writer and director do a great job of setting the tension with the "haunted house" sort of feel that the episode brings, making you jump with what might be lurking around the corner. Suchet is fantastic as the dodgy landlord and adds to that feeling.

Capaldi and Mackie are excellent as usual, and it's fun to continue to watch their characters' friendship grow, as well as them banter. Bill continues to learn more about the Doctor along with any new audience as he talks about being a Time Lord and jokes around about big collars, which is another enjoyable reference for fans. The Doctor also felt more true to his old self to me in this episode than compared to last week.

The creature makeup was fantastic in the episode and brought the perfect balance of beauty and horror.

I of course also appreciated more in the way of "the vault" story, as it starts to become clearer who might be inside.

All in all, another terrific episode that makes me wish Capaldi wasn't leaving soon.