TIME TRAVEL, Highland rebellion, steamy romance and visceral violence. Outlander has now become as synonymous with Scotland as tartan and shortbread across the globe. The show, based on the novels by American writer Diana Gabaldon, sees World War II nurse Claire Fraser travel back in time to the Jacobite risings of the 1740s. It has millions of viewers on both the Starz channel in the US and on Amazon Prime Video in the UK, multiple awards and a devoted fan following - it's also turned into a cash cow for the Scottish tourism industry with Outlander tours booming. With the third season hitting our screens last week and the fourth about to start filming on our doorstep, we bring you the ultimate catch-up. From the plotlines to the frocks, and from the feminist critics to the ultra-violence, here's what you need to know.

1. The plot...and the stars

Outlander is not short on plot. In brief: 1940s English nurse Claire Fraser, played by Caitriona Balfe, leans absent-mindedly on a standing stone while honeymooning in Scotland and finds herself hurtling back to 1743. Life my be tough in 18th century Scotland, but having just survived a modern war, the tenacious Claire take its brutality in her stride and catches the eye of young Highland warrior Jamie Fraser, played by the strapping, kilt-wearing Sam Heughan. He is not adverse to stripping off – and she is not adverse either.

Unfortunately she also catches the eye of the show’s arch-villain, Captain 'Black Jack' Randall and so - despite having a modern day husband in the 20th century - marries heartthrob Jamie. Marriage is no safe haven though as Claire is soon accused of witchcraft and Jamie brutally raped in scenes which shocked fans. However, they are reunited and escape to France, where Season 2 is set - many swashes are buckled and the battle to free Scotland from the Red Coats goes on. Claire returns to the 20th century, and season three opened last week with her contemplating her future - and the pain for separation from Jamie...as a mother to a teenage daughter in 1960s Boston.

It might sound exhausting, but TV audiences have been lapping it up. In June this year the series arrived on free-to-air TV channel More4 to a record-breaking audience of over a million viewers, following similarly strong figures on Amazon Prime Video. As a result Balfe and Heughan have become big names in recent years with star status and celebrity endorsements to match.

2. The source material

In the late 1980s Diana Gabaldon, inspired by that other famous time traveller Doctor Who and intrigued by whether she had what it took to pen a novel, sat down to write Outlander. She claims she never intended to show it to anyone. It turned out to be the first of what is to date a nine-strong series of books, which straddle almost as many themes as they have devoted fans.

The first seven books sold over 20 million copies before syndication rights were snapped up and a screen play developed by Ronald D. Moore –famous for his work on Battlestar Galactica and Star Trek Next Generation – and produced by Sony Pictures Television and Left Bank Pictures for Starz. Gabaldon, formerly a research professor at the University of Arizona, is both co-producer and consultant.

3. The fashions

The characters may be larger than life but the costumes also take centre stage. For costume designer Terry Dresbach, who is also the wife of executive producer Ronald D Moore, detail is all. Outfits are hand dyed, painted or aged and even the buttons are embroidered. Every female cast member wears a corset, and the men wear nothing underneath their kilts. Twelve versions of Claire's main 18th century dress were made, and a total of over 10,000 garments were made for Season 2 alone – there are so many costumes Dresbach and her team use a digital filing system, called Mother, which sees every costume bar coded, logged on the computer, and stored accordingly. The fashion influence has not only spilled on to the catwalks but spawned an Outlander clothing line.

4. The fans

From the Caitriots, Heughligans and Menziatics (devotees of Balfe, Heughan and Tobias Menzies, who plays the shows super-villan Jack Randall) to the US based Outlander Addiction and the Outlandish Bakers, who track down the cast and crew onset to deliver homemade sweet treats, this is a phenomenon with some serious super fans.The stars provide plenty to satisfy their ardour, interacting with fans on social media and even appearing at Outlander conventions and other events. The Sunday Herald was even graced with Balfe and Heughan as guests at our Culture Awards.

Angela Sasso, of UK fan club Outlandish UK, which now has over 2700 members, says fans from around the world are initially drawn together online through their shared love of Outlander but often go on to form meaningful friendships. Outlandish first decided to hold a gathering for members in 2013. "The idea was for lunch and a walk in Edinburgh," she says. "We had so much interest it ended up a three day event attended by 110 people." Since then there have been a further two meet ups, both attracting over 200 people. This year's involved visits to locations as well as a surprise appearance by Richard Rankin who plays Roger Wakefield, the love interest of Jamie and Claire's daughter Brianna Randall. Being a super fan has been a hugely positive experience, according to Sasso. She enthuses: "We are here to support the books, the production, the actors because they are doing a fabulous job and we just want it to continue."

5. The fantasy and the feminism

It's been described as a "bodice ripper" and a "guilty pleasure" but according to Dr Faye Woods, a television researcher at Reading University, the reason people are sniffy about Outlander is that it concentrates on the concerns of women. "Think about Harlequin romances and Mills & Boon and how their engagement with female desire is dismissed culturally," she argues.

Sex and female pleasure are at the very centre of Season One – Claire takes control in the bedroom – but Woods claims many reviewers don't know what to make of this aspect. "As a culture we’re still not really sure how to talk about texts that centralise or explore the complexities of female pleasure and desire without trivialising it," she adds.

Jorie Lagerwey, lecturer in television studies at University College Dublin agrees. "TV critics are often invested in prestige or so-called 'quality' television, which means things that seem to tackle contemporary social issues, look really expensive, have big ensemble casts, and multiple, complex ongoing storylines," she says. "They also are almost always about men." Funnily enough the women centric plots don't put off men – who make up about 50 percent of viewers – from watching Outlander.

6. The sexual violence

Outlander is not for the faint hearted. There is a lot of horror and rape, often prolonged and graphic. The brutal rape of Jamie in a torture chamber by Captain Randall is one of the show's most infamous to date. Some have found it simply shocking, others have considered it in a less literal sense claiming that it is written as a metaphor about England's brutal behaviour towards Scotland in the 1700s. To Dr. William Proctor, an expert in popular culture at Bournemouth University the lack of controversy about the scene is surprising. Certain representations of rape in fiction, such as the sexually assault of Sansa Stark in Game of Thrones, attract a large amount of controversy while Outlander has not been vilified in the same way, he says. "From a different perspective, it is important that male rape is represented across media platforms as it something that is quite often by-passed."

7. The locations

Though Gabaldon's books are set in Scotland, originally the production team considered shooting in New Zealand and Eastern Europe. In the end most is shot in and around the Highlands with Glasgow - which doubled for Boston - and Edinburgh having their moments in the sun.

VisitScotland figures showed tourism received a corresponding boost. Between 2014, when Outlander first aired, and 2016, Doune Castle (Castle Leoch in the show) enjoyed a 91.8 per cent increase in visitors, from 47,069 to 90,279. Blackness Castle, the setting for malicious Black Jack Randall’s HQ, has welcomed 85.3 per cent more visitors since 2014.. Outlander tours can now be found across the country.

Jenni Steele, film and creative industries manager at VisitScotland, claims the level of interest shows no sign of slowing down. "It's really caught the imagination," she says. "It's about Scotland's heritage and history and it's filmed on location so it's been a real boost for us."

As well as creating interest in locations she claimed Outlander's themes had also had an impact. "There's been an increase in interest in genealogy and clans," she adds. "It's emotive stuff and it really connects people to Scotland."

8. How it could have led to an independent Scotland

It might seem like it's just a great big romp of a TV drama, but with its Jacobite plotlines and its stars supporting Scottish Independence, David Cameron was far from a fan back at the time of the referendum. Leaked emails published by Wikileaks revealed that he'd met Sony representatives ten weeks before the referendum on Scottish independence to discuss the UK release date, which it was rumoured was due to be screened in the autumn of 2014.

The email, sent from Sony vice president Keith Weaver to chief executive Michael Lynton and other senior Sony figures, outlines the agenda, with particular reference to Outlander's importance "vis-à-vis the political issues in the UK as Scotland contemplates detachment this Fall". In the end it went out in March 2015. We'll just never know if an earlier transmission date could have changed history.