Since Doctor Who returned in 2005, it has featured many big name actors from the world of television and film. Bernard Cribbins, Michael Gambon, Timothy Dalton and many more have made guest appearances...yet David Suchet, arguably one of the country's most famous TV actors, has not starred in the show before now. For this reason alone there was quite a lot of buzz surrounding Knock Knock, the fourth episode of Series 10.

Did it live up to the hype?

The answer to that question is a resounding yes.

Knock Knock sees Bill (Pearl Mackie) searching for student accommodation with her friends Shireen (Mandeep Dhillon), Harry (Colin Ryan), Paul (Ben Presley), Felicity (Alice Hewkin) and Pavel (Bart Suavek). After a number of failed attempts to find somewhere suitable to live, Bill and company are on the verge of giving up when they are approached by The Landlord (David Suchet), who believes he has a suitable property. It's dirt cheap and its rooms are very spacious. The group sign a contract to stay in the house, but it soon becomes clear that all is not what it seems. There's no central heating, the plug sockets are old and they are unable to pick up a mobile signal inside the house. There are also some very strange noises during the night, and Pavel hasn't left his room since they arrived. The Doctor (Peter Capaldi) is curious, and decides to investigate.

I haven't been scared by Doctor Who in a while. The last Doctor Who episode I found genuinely horrifying was 2009's The Water of Mars. This isn't intended as criticism towards the show, it's just that I am older now than I was in 2009 so I am not scared as easily as I was before. Knock Knock, however, absolutely terrified me. The sound design in this episode is spot on, with lots of tense music and creepy creaking noises creating a typical horror atmosphere. There is a binaural (3D surround sound) version of the episode available on iPlayer; I haven't tried it, although I could imagine it adding a nice extra dimension to the episode. Knock Knock's use of sound is very effective without the binaural surround sound though, and helps make the show's latest attempt at a haunted house its most successful by far.

It helps that this episode's writer is Mike Bartlett. As a playwright, Mike Bartlett will no doubt he used to writing small self-contained stories that use a single setting for maximum impact as opposed to the bigger scale stories of the new series such as The Stolen Earth/Journey's End or The Day of The Doctor. His experience as a playwright therefore shows through in Knock Knock in the way his script plays with the horror behind the unexplainable strange sounds many of us often hear during the night in our own homes. In Knock Knock's case these sounds are explained to be alien woodlice the Doctor calls 'Dryads' entering through the woodwork to feast on whoever is currently living inside the house. Unnervingly their victims also become a part of the woodwork once consumed, which is a surprisingly dark concept after the lighter episodes of Series 10 (The Pilot, Smile and Thin Ice).

Of course, some will complain that the actions of Bill's friends are stupid. I've already seen some comments about how you wouldn't buy a house with so much wrong with it, or you would be a bit more concerned if somebody had stayed in their room for a day and never left like Pavel. I would point out however that characters doing stupid things is a trope of horror. Look at The Blair Witch Project, for instance. The filmmakers all act dumb in that, but that's what allows the horror situation to escalate. The actions of the characters in Knock Knock just show how much Mike Bartlett understands on how to make a scary episode of Doctor Who. This is a guy who clearly knows exactly what he's doing, who clearly has a deep understanding of genre and who clearly (in my opinion at least) should be invited back to write for the show again.

The cinematography of this episode is fantastic, its moody and atmospheric lighting helping to successfully convey the familiar haunted house aesthetic. The Director of Photography Damian Bromley should be applauded for the visual aesthetic for this episode, which conveys the tone of previous haunted house episodes such as Ghost Light and Hide. Shadows are cast over the actors' faces, and the camera work often tightly framed to give an almost claustrophobic feel that works well with a hide-behind-the-sofa-style episode of Doctor Who.

Pearl Mackie continues to impress, but the highlight of the episode is David Suchet as The Landlord. David Suchet is a revelation in the role, and gives possibly the best guest star performance since Michael Gambon in A Christmas Carol. I was so impressed by The Landlord, in fact, that I started a petition to bring the character back (https://www.change.org/p/doctor-who-...ter_responsive). The Landlord is a captivatingly creepy, sinister villain and the payoff with his character at the episode's conclusion puts a lot of his behaviour into perspective. It is understandable why he's feeding students to the Dryads, but unlike the previous three episodes' monsters/villains he isn't a misunderstood character. His actions are still evil - feeding students to some alien insects is still wrong, even if it is to keep his mother alive.David Suchet plays 'evil' very well, and I hope they can find a way for him to return.

My only complaint about this episode is that again, Matt Lucas only appears briefly at the episode. I'm not the biggest Matt Lucas fan, but he is being completely wasted in his role on Doctor Who so far and I wish the writers would feature him more so I can form a proper opinion on Nardole other than indifference. Nardole's cameos feel strangely like Steven Moffat owed Matt Lucas a favour than the character having any sort of narrative reason to be included in Series 10. His role so far amounts to moaning at The Doctor because he's not staying on Earth to protect the vault, and it comes across as more of an awkward intrusion on the episode than a scene you particularly look forward to in each story.

Overall, Knock Knock is a very creepy episode of Doctor Who and one that I reckon will be considered a classic in ten years' time. Mike Bartlett's debut as a writer for the show is possibly the strongest since Jamie Mathieson with Mummy On The Orient Express, and I certainly hope that he will write for the show again. The combination of Mike Bartlett's writing with the excellent sound design and dark cinematography allows for an episode that perfectly captures the 'haunted house' feel, more so than 1989's Ghost Light or 2013's Hide. David Suchet is the one standout element of the episode however; he is fantastic as The Landlord and gives the strongest guest star performance since Michael Gambon 2010's A Christmas Carol. Knock Knock is without a doubt one of the greatest episodes of the Peter Capaldi era so far, written by one of the show's greatest guest writers.