Doctor Who Series 10: 7 Big Questions After 'Knock Knock'

The last three episodes have all ended with a brief cameo of Nardole and the vault. The pattern is in danger of becoming a little too repetitive but fortunately in two episodes’ time all will be revealed, and with the shot of the Doctor’s face in front of the opened vault we’ve probably seen the final tease.

Many fans think that they’ve already worked it out.

The prisoner is no stranger to the Doctor – the piano and the Mexican takeaway would have been wasted gifts otherwise. The Doctor has been guarding the vault for several decades now, so feasibly the pair could have developed a relationship over the years, but there is a level of empathy that suggests a deeper connection. He understands just how hard the prisoner’s loss of freedom must be, which would of course apply to anybody trapped inside, but the fact that the Doctor seems particularly guilty about continuing his travels in space and time heavily implies that the occupant is a fellow time traveller.

A bigger clue is the prisoner’s gleeful reaction to the gruesome tale of humans being eaten. Other than the Master, is there really any other Time Lord who could have such twisted tastes? Remember how the reborn John Simm Master woke up with an insatiable appetite for all things organic (The End of Time)?

Eagle-eyed viewers will have also noticed that in the series ten trailer, Missy can be seen lying seductively on a grand piano. The songs the prisoner play (Fur Elise, Pop Goes the Weasel) seem right up her street. So the one remaining question appears to be which version of the Master is inside the vault.

A straightforward, unsurprising reveal would be in keeping with the style of the series, so another twist, such as it being the next Doctor or Susan, is unlikely. But let’s not put it past Steven Moffat to have made the vault and it’s occupant a big distraction. Perhaps the real threat is already outside.

What questions did Knock Knock leave you with? Let us know down in the comments.