Even before the first clanger of a pun had been dropped, it was clear that Wednesday's episode of The Great British Bake Off would be a dramatic one. The previous show had ended on a preview of judge Mary Berry's noncommittal "that's sort of unacceptable", which only in the twisted world of Bake Off could be a thrilling portent. Rumours quickly began circulating of a great betrayal – an act of deceit that would out-scandal even the great custard heist of series four.

And the scandal did not disappoint. It was everything a romantic could have hoped for: an old country house, heartbreak, melodrama, futility and a tormented, bearded young man striding moodily through the English countryside. A nation wrung its hands in glee. It was Iain, a construction engineer, at the centre of the drama. He was already off to an inauspicious start when, peering over at his black sesame ice cream, 79-year-old Mary – confused by any ingredient that can't be found in Mr Kipling's – quizzed: "Mushroom soup?" But as Iain's hopes slowly unravelled, it was fellow baker Diana's (alleged) treachery that seemed to seal his fate, as she took his sludgy ice cream from the freezer to make room for her own.

Twitter was instantly aflame. The revolt was two-pronged: many viewers, and some of the less scrupulous ex-bakers, called for "Justice for Iain"; others simply went straight for Diana. To see the remarks in isolation – "she's evil", "drown her", "stone her" – you could be forgiven for thinking that they're quotes from the Salem witch trials – not a hate campaign against a 69-year-old WI member and amateur baker from rural Shropshire.

Since then, Diana has tearfully gone on local radio to hint at a "stitch-up" and Bake Off presenter Sue Perkins has waded in to insist that the ice cream was barely out of the freezer for 40 seconds. All of the contestants have rallied to Diana's defence, including ill-fated Iain. None of this matters though, of course, because the narrative that was propagated and has now taken hold in the public's consciousness is one of demonic Diana, deceitful Diana and – the unnerving Twitter trend so far – dirty Diana.

To add yet another layer of intrigue to this melodrama, it's been revealed that Diana won't return to the tent again. Illness has been cited as Diana's reason to drop out of the competition, although it's a move that will no doubt come as confirmation of her guilt to those who set a ransom upon her head.

I'm gutted to see her go. Shame on the online lynch mobs and on the show's editors for letting a jolly Shropshire lass's Bake Off dreams end in a witch-hunt. The only consolation is that she's not on Twitter to see what's being said.

We'll never know exactly what happened in that tent but I'd hazard a guess that apart from a few over-zealous hockey tackles many years ago at school, Diana's likely to have never done a malicious thing in her life. If there was nastiness in the tent this week, it came in the form of making a humiliated Iain parade the dustbin – into which he'd dumped his baked alaska – to the judge's table. Nastiness was spinning a story that cast an old lady as a pantomime villain. Nastiness was setting a challenge as embarrassingly retro as baked alaska in the first place.