Knock Knock sees the Doctor and Bill get embroiled in trouble back in present day earth at Bill’s new house. She moves in with her friend Shireen, and four other housemates, in a large house rented to them by a man known only as The Landlord (David Suchet). The Doctor is almost immediately distrustful of the house and stays to investigate, against Bill’s wishes.

This was an episode that had huge potential based on the ‘next time’ teaser at the end of Thin Ice. The trailer set Knock Knock up as a horror, almost haunted house esq, episode. And the first half of Knock Knock really felt as thought it was going to go down that route. There were some creepy moments, but not enough. The episode veers off that course wildly when it gets into the second half. Despite setting up what could have been a great creepy horror episode, it never really comes to fruition. Instead the ending becomes a quite tragic story revolving around The Landlord.

Firstly it “kills off” all the supporting characters way to fast (although slightly cops out of this at the end). There’s nothing in the episode to really make you care about them because they just don’t get much screen time. Maybe if this had been a two-parter it could have worked much better. Everything in this episode felt rushed, the character’s deaths, the move away from horror before it truly gets creepy. If it had been a two-parter with a full on horror episode, in the vein of The Empty Child or The Silence In the Library, then it could have been fantastic, because the ending actually has a very strong emotional payoff to it.

David Suchet is fantastic in the villainous role. The tragic story of him with his mother, who believes she is his daughter, is the best part of the episode. Although his role as a villain is slightly tarnished by how unthreatening and rubbish the monsters are. They are revealed far too early in the episode, and when they are it is such an anticlimax. Space lice. They felt like such a let down once they were revealed because of they just were in no way scary, and couldn’t live up to the horror premise that the first half of the episode gave us.

Finally we get a lot more of information regarding the vault. We can take it as confirmed that the vault contains someone, because we hear someone playing the piano from inside. The Doctor then offers to have dinner and tell him the story from the episode. The smart money would be on The Master being inside the vault (whether Missy or John Simm’s version is hard to say), but you never know Moffat may yet throw out some surprises.

After a very strong start to the season this episode felt like a lot of wasted potential. Despite a great performance from David Suchet, this episode felt like one that would have worked much better as a two-parter. It wasn’t scary enough, we didn’t care about the supporting characters enough, and the monsters were very anticlimactic once they were revealed.