“She is coming!” cried Thesea, and she ran forward to meet the beast. The seven bachelors shrieked, but tried to stand up bravely and face their fate; and the six young women stood together with firm-set teeth and clenched fists, ready to fight to the last.

You might recognise the story, but something’s different. We’re in Crete, where Queen Minoa keeps a beast in a labyrinth. Thesea has been sent from Athens to be devoured in a terrible act of vengeance. But – spoiler alert – the brave heroine slays the beast, then uses a previously unravelled thread to find the way out of the labyrinth to freedom. The beast, incidentally, is the Minoheifer.

And now you see what’s going on here. Gender-swapping, thought-provoking, and charmingly rendered by wife-and-husband team Karrie Fransman and Jonathan Plackett, for their latest book, Gender Swapped Greek Myths. She’s a comic artist, he’s a “digital inventor” who has made an algorithm that changes the genders of characters in stories (kind of like find-and-replace, but there’s a bit more to it).

Plackett’s dad used to swap the genders of the characters when reading to him and his sister as kids. “I think to make it more interesting for my sister, but also for himself as well,” he says.

They’re talking to me on a video call, sitting on their bed, “like John and Yoko”, laughs Fransman, letting slip a little unconscious bias, which she readily confesses to. It comes out when she’s with her four-year-old daughter, too, “referring to animals as male – Hello Mr Magpie – or assuming the school photographer is a man, and I think I’m a switched on card-carrying feminist!”

Their first daughter (there’s now another, aged 10 months, currently being looked after by a grandad) was also a catalyst for the project. “We were thinking about the kind of messages she was getting from the world and how to rebalance them a little bit,” says Plackett.

Their first book was Gender Swapped Fairy Tales. “Because they are a big influence on the way children think and are brought up,” he says. “They form the early building blocks of the expectations on you. And it was an easy place to start because they are so gendered.”

So kings became queens, brave princesses rescued imprisoned princes, and a scary she-wolf jumped out from behind a tree into the path of a pretty boy wearing a red hoodie. There’s nothing especially new about strong female characters grabbing the reins from traditionally male roles; Fransman and Plackett point to the Pixar film Brave as a good example. More surprising, and perhaps more interesting, is what happens when the algorithm spits out new men. “We noticed in our stories there were suddenly lots of men who really wanted to be fathers,” says Fransman. “And really great fathers.”

That’s something that Plackett recognised. They had issues having kids and went through IVF. He desperately wanted to be a dad, twice. But that guy wasn’t in kids’ books, with the possible exception of Geppetto in Pinocchio.

The Greek myths, with their peak patriarchy, dramatic power imbalances and raging toxic masculinity, pretty much demanded to be fed into the gender-swapping algorithm. Fransman and Plackett used public-domain versions of some of the better-known stories, from the late 19th and early 20th centuries, that had been abridged for children. That means some of the things that might have been interesting seen through their magic mirror – Tiresias’s actual trans journey, the story of Iphis and Ianthe, Heracles’s gay adventures, Zeus’s serial rape crimes – don’t feature, and the result probably shines a light on the attitudes of 150 years ago as much as on the ones of 3,500 years ago.

That doesn’t mean the exercise isn’t valid – it’s not as if there isn’t enough still there that needs that light shone on it. Plackett’s original idea, in fact, was to do it with newspaper articles, prompted by a report of a meeting between Theresa May and Nicola Sturgeon that focused chiefly on their legs, and how that would look had it been applied to David Cameron and Barack Obama. “Once you get your gender-swap goggles on and start looking at the world, you notice a lot of stuff.” That includes what his elder daughter watches too. “It’s always the male characters fighting and rescuing people and the female characters getting saved. Even if they are heroes, they are not as violent as the male ones.”

Fransman enjoyed the women who came out of the gender swap. “We now have these super-macho women, Thesea and Odyssea; they’re just awful. I don’t think I realised how badly behaved they were. I mean, Odyssea condemns her entire crew to death because she cannot not boast to the Cyclopsess. When people think of Odysseus and Theseus and Perseus, the male versions, I don’t think they think of them as psychopaths.”

Interesting. How do you turn a hero into a psychopath? Turn him into a woman. “It was shocking and exhilarating. It was so exciting to be able to draw these beastly, huge, grotesque women I’m not seeing represented on TV and film and in other books.” Her wonderful illustrations, influenced by the Greek sculpture from the classical and Hellenistic periods, help to weave the text of stories – some of which are stylistically different because of the different source material – together into something cohesive. I particularly like that Cyclopsess – a hairy-legged giant with a monobrow over the wound where her one eye used to be, hurling rocks and abuse at Odyssea’s departing galley.

Again with the illustrations, it’s some of the female-to-male swaps that throw up the surprises. Fransman unearthed loads of original images and classical paintings of Persephone being carried off by Hades. “What I found really interesting is that she isn’t fighting back in any of them, her arms are just flailing, she’s not digging her nails into him, she’s not trying to get away.” So that’s how she drew it after swapping them: big, strong, male Persephonus being dragged off by Hadea like a rag doll.

Fransman and Plackett bat away any accusation that they’re sanitising the classics. “It’s hardly a utopia,” says Fransman. “It’s still an unequal world, just flipped. Why would we advocate that women should go out and take a lover, carry men off against their will? It’s very unequal and dark. We want to bust the binary, look at the very idea of masculinity and femininity.”

In a way, though, their gender-swapped Greek myths are still binary, just binary flipped; certainly, they are heteronormative. But the pair believe that by swapping the two dominant gender constructs, the division will be disrupted and this will get us all thinking about how gender defines everyone and everything. “It’s more important for us to make people think about the current world and how it could be different,” says Plackett.

So they have done fairy tales, and now Greek myths – what’s next, I wonder, a gender-swapped Bible, perhaps? Classic literature, Jane Austen might be fun, Marvel, Paw Patrol? They are constantly on the look for stuff to feed into the gender-swapping machine, says Fransman. Shakespeare – Romy and Julian? Plackett admits they have had a little bit of a play with that one. How did it go? “It still didn’t end well for them,” he says.

• Gender Swapped Greek Myths, by Karrie Fransman and Jonathan Plackett, is published by Faber (£20). To support the Guardian, buy your copy from bookshop.theguardian.com. Delivery charges may apply.