How Doctor Who's The Haunting of Villa Diodati contradicts canon – but also doesn't

The Haunting of Villa Diodati sees the Doctor (Jodie Whittaker) and the gang arrive at the titular manor on the evening that, as legend would have it, inspired Shelley's Gothic novel. The Time Lord is of course aware of Mary's works, as well as those of her contemporary Lord Byron (Jacob Collins-Levy), but there's no reference to the pair having met before – Mary (Lili Miller) certainly makes no reference to any prior encounter.

Mary meeting a half-finished Cyberman will, we're led to understand, provoke her to write Frankenstein – she even refers to Ashad (Patrick O'Kane) as a "modern Prometheus" and her finding the humanity in this 'monster' can also be seen as a precursor to the sympathetic portrayal of the tragic monster in Shelley's book (and subsequent adaptations).

• Doctor Who: the real story of Shelley, Byron and the Villa Diodati

The trouble is, Doctor Who has been here before – in a series of stories released by audio drama producers Big Finish between 2009 and 2011, the Eighth Doctor (Paul McGann) meets Mary (played by Julie Cox) during her stay at Villa Diodati and she briefly becomes his travelling companion. October 2011's The Silver Turk even has Mary meet a damaged, malformed Cyberman and take pity on the creature... inspiring her to write Frankenstein in 1823.

How, then, can we possibly square these two contradictory accounts of the Doctor's first meeting with Mary and the genesis of Frankenstein?

The easiest solution would be to argue that only televised Doctor Who counts as canonical, that Big Finish 'doesn't count' – except the Paul McGann-starring minisode The Night of the Doctor from 2013 had the Eighth Doctor, on-screen, explicitly reference companion characters who have only appeared in audio stories. Steven Moffat, then, appears to consider Big Finish to be canon, and who are we to argue?

So how do we get around this continuity clanger? Well, interestingly, The Haunting of Villa Diodati itself might hold the answer...

As the story nears its dramatic climax, team TARDIS are faced with a moral quandary – should they allow Percy Shelley (Lewis Rainer), who's been infected with powerful artificial intelligence the Cyberium, to die so that billions in the future might live?

Ryan (Tosin Cole) suggests it's the right thing to do, that it's one life against billions, but the Doctor tells him that Shelley's death, and the resulting absence of his literary works, could have a huge impact on "future history".

"History will change in a blink," the Time Lord says. "The future will not be the world you know. The world you came from, the world you were created in, won't exist. So neither will you!"

Here we might have the key to explaining how two different versions of Mary meeting the Doctor and the Cybermen for 'the first time' can co-exist.

The Cyberium, and Ashad, being sent back into the past changed history – we know that much for certain. The moment that happened, Mary's future was changed, which would mean that the previous Mary, the one who met the Eighth Doctor and travelled with him, no longer existed.

This isn't to say that those adventures never happened exactly – from the Doctor's perspective, they very much did. But the changes to history seen in The Haunting of Villa Diodati could mean that Mary's life took a different path, one in which she never met another Doctor or a different Cyberman. (Though the TV version of Mary clearly has never met the Doctor before, there's nothing to suggest that the Doctor hasn't met her before – maybe she's just keeping quiet about their past acquaintance so as not to disrupt history any further.)

It's a theory at any rate – and given that Doctor Who has always played pretty fast-and-loose with exactly how time travel works, we'll be considering it canonical until another plot twist tells us we're wrong...

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