It’s time to talk historical drama’s most unlikely sleeper hit. Yes, even more unlikely than a series following a cheekboned crime-solving 1950s Anglican vicar (ITV’s Grantchester) or one entirely based on Tom Hardy’s penchant for brutish skulking and indecipherable dialogue (ahem, the BBC’s Taboo). This is the story of Claire (Caitriona Balfe), a 1940s Englishwoman who, having worked as a nurse during the war, takes a belated honeymoon to Inverness where she travels – bear with me on this – through some standing stones to 1745.

If the eighteenth century is all pristine drawing rooms and delicate coiffures to you, then you’ve probably been spending too much time in Georgian London. Up in the highlands of Scotland, it’s a very different story. It’s a land of draughty castles, medieval-looking blankets, narrow tracks, and deep-seated rumblings of revolt. Though Claire’s Forties medical knowledge looks outdated to us, in 1745 Scotland it makes her practically unearthly. It gives her already outspoken character a great deal of purpose (when she’s not being accused of witchcraft for trying to introduce things like stitches, hotchpotch remedies and baths to stubborn Scotsmen). There she negotiates belligerent clans and wall-to-wall tartan, falls in love with young Highland warrior Jamie (Sam Heughan), and tries to stop the ill-fated Jacobite Rebellion.

This may all sound a bit bad-cover-bodice-ripper, but the titular novel series by Diana Gabaldon – on which Starz’ adaptation is based – sits fairly comfortably in the genre of detail-heavy historical fiction. First published in 1991 and with fans often waiting four or five years for the next book, in literary terms, Outlander is historical time travel’s answer to Game of Thrones. It deals with some fairly Thronesian subjects too, and with six of at least nine books still to cover, the television adaptation is unlikely to outstrip its source material any time soon.

The series is made even weirder by what could perhaps be described as odd choices in settings and plot twists. Large parts of the second series subject us to the frankly horrifying fashion of 1960s Scotland (there’s a disturbing amount of mustard and brown), and later books expand to take in colonial America. You can almost understand why bewildered television executives may have struggled to get their heads around it. Throw in its defiant centering of a female lead and a notable use of the female gaze in a male-dominated genre, and it’s unfortunately little wonder that terrestrial television has been slow off the mark with this one. Complete with a refreshing change to the troublesome Hollywood age gap (Balfe is older than Heughan), Outlander just doesn’t fit the standard criteria for ‘predictably successful historical drama’. Now scrambling to catch up, UK broadcasters have been left looking a little red-faced. In acclaim and ratings alike, Outlander has been delightfully popular; fans seem to relish the show’s strong accents, bustling plot, detailed cinematography, vigorous relationship dynamics and sheer sexual tension.

Even Irish broadcaster RTÉ got there relatively early with this one, though lead actress Caitriona Balfe – who has won Saturn Awards and a Scottish BAFTA, as well as Critics’ Choice Award and Golden Globe nominations, to name just a few – has never won an IFTA, making her name unusually more known outside Ireland than within. Still, if you haven’t watched Outlander yet, this may be the time to jump onto the bandwagon, with a third season to air later this year and a fourth already commissioned. After all, this is the series that manages to make kilts look cool.

You can catch Outlander on Thursdays at 9pm on More4.