HOW IT BEGAN

We would never have had Jimmy Perez on screen at all if it wasn't for a TV producer called Elaine Collins walking into a second-hand bookshop in North London. Here, she found one of the Shetland crime novels by Ann Cleeves. An award-winning author, Cleeves had written the first of her Shetland-based whodunits intending it to be a one-off rather than a series - her reasoning being that nobody would accept a succession of murder cases in quiet Shetland. But the book's incredible success persuaded her to come up with more stories about her hero Jimmy Perez, giving Shetland a body count comparable to a violent inner city (or Midsomer, in fact). On accidentally discovering the books, Elaine Collins knew they were ripe for the telly treatment and everything followed from there.

CHANGES TO THE LEAD CHARACTER

One big difference between the books and the TV series is the appearance of our lead character, the doggedly determined detective Jimmy Perez. As his name suggests, he's supposed to have Spanish ancestry and, in the novels, he's described as olive-skinned and rather swarthy, with wild black hair and a kind of exotic "otherness" to him which makes him stand out among the locals of Shetland. The TV Jimmy is an altogether different sort of chap, played by the noticeably fair-haired and non-exotic-looking Douglas Henshall. Fans of the novels have been won over to this interpretation though, with Ann Cleeves herself saying "He doesn't look anything like my Jimmy, but Douglas is quiet, authoritative, and a little bit edgy."

INVENTING A SIDEKICK

One of the best things about Shetland is the mentor-protégé interaction between Jimmy Perez and his fellow cop, Alison "Tosh" McIntosh. She's the perfect plucky foil to the older and more weather-beaten Perez, and the whole show would feel a little empty without her. It may, therefore, come as a surprise to viewers to learn that the character of Tosh doesn't actually exist in Cleeves' original Shetland novels. Tosh was, in fact, created for the TV series, which sounds like quite a liberty. But fortunately, Cleeves was absolutely fine with that, and has in fact gushed about the effectiveness of Tosh, saying in one interview that she wished she'd written the character first.

TELLING THE STORIES

Like all great adaptations, the Shetland TV series is bold enough to go its own way with the source material, rather than stick pedantically to every aspect of the originals. Ann Cleeves has said that the telly version isn't faithful to the intricacies of her plots and characters, but is very faithful to the spirit of her stories. If you're a fan of the books, one of the incidental pleasures of the show is detecting the traces of Cleeves' original story arcs and seeing how they've been cleverly tweaked for the small screen.