Acclaimed playwright Mike Bartlett writes a very impressive script that manages to juggle a lot of narrative balls successfully.The Doctor’s presence means that each shocking event is a learning experience, rather than culminative displays of stupidity by the characters and, as we learn more about the situation, we learn that it is more than a madman luring and killing people, rather a more tragic tale of the devotion between parent and child – and who fills what role.
"Knock Knock" is, of course, lower budgeted than even a modest feature film of this genre. Yet there is one thing that this story has over the vast majority of cinematic shockers – a villain portrayed by an actor of David Suchet’s calibre. Suchet’s underplaying of the role means that he can seem like a slightly odd old man with a big house that anyone would have no problems with trusting. Yet the sheer craft that Suchet brings to the role means that depths are opened up with each revelation that belie the subtle changes in his performance. The regulars are on fine form and their interplay perfectly utilises the dynamic between the alien genius and the untutored, but perceptive intelligence of the companion. We must also not forget a very fine performance from the excellent Mariah Gale as the tragic Eliza and, indeed, our clutch of foolhardy teens. Credit must be given to director Bill Anderson for using this marvellous cast so well and he does not take his eye off the ball visually, with some very memorable scenes and a very confident production – the image of the wooden Eliza is incredibly striking and such shocks as Pavel being trapped and the Dryads devouring their victims. The Dryads become less threatening once they are revealed, but this is probably to the story’s purpose and makes the restoration of Bill’s housemates acceptable in story terms. Perhaps more so than any story since "Midnight", the sound mixing is crucial to its success, and the special binaural mix makes it an unforgettable headphone experience.
"Knock Knock" is wonderful entertainment and a fine example of something Doctor Who has done well for decades – taking a well-worn genre staple and making it something else entirely.