These UK islands feel more Scandinavian - and their history is full of surprises

I arrive on Shetland happy but with murder on my mind. Don't worry, I'm not plotting anything. I'm just thinking about Shetland, the long-running TV crime drama that's filmed across this ruggedly beautiful outpost of Britain, where the Atlantic Ocean buffets the North Sea. Thankfully, these occasionally tempestuous waters are mostly placid for our (northern) spring cruise, which has us calling in at a string of Scottish islands.

Shetland, also known as Mainland, is the largest of the Shetland archipelago. We're still in the UK, but it feels, in some ways, more like Scandinavia (as the gulls fly, we're closer to Bergen in Norway than Glasgow, Scotland's biggest city, where our voyage began). From my cabin balcony, I spot, sprinkling the hillsides above the wee Shetland port town of Scalloway, the kind of colourfully-painted timber-clad houses you see in Norwegian, Danish and Swedish coastal villages. Below us, meanwhile, a brawny port worker with an impressive russet beard looks like a character from another TV hit, Vikings. I wonder if his ancestors were on the dragon-prowed longships that sailed here from Scandinavia more than a thousand years ago.

We hop off Le Boreal, our sleek Ponant vessel, and take a coach ride south of Scalloway, twisting past misty, sheep-grazed farmland, glacier-carved valleys and precipitous cliff edges. I deduce that you don't need to have watched one single episode of Shetland to appreciate this is the ideal backdrop for murky mysteries. Adapted from Anne Cleeves' detective novels, the show has similar vibes to classic Scandi noir TV series like The Bridge and The Killing. Our local guide, Gill Nadin, reveals that the Shetland Islands were ruled by Norsemen for 600 years until Scotland claimed them in 1469 CE.

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The Nordic influence lingers in everything from the DNA to the culture. The most celebrated annual gathering across the 16 inhabited Shetland Islands is January's Up Helly Aa, a winter fire festival featuring torch-lit processions and the burning of a replica Viking longship. After passing road signs for Scandi-sounding villages like Gulberwick, Skellberry, Boddam and Virkie, we cross a road traversing the runway of the island's tiny main airport, which receives about 30 planes a day from the UK mainland. Some carry passengers working in the North Sea oil and gas industry that transformed Shetland's economy in the 1970s.

At nearby Jarlshof, Gill vows to take us "time travelling". Hugging a picturesque sandy bay, this is not only Shetland's most significant historic attraction, it's apparently the most important multi-period archaeological site in all of Europe. Gill explains Jarlshof was settled continuously for about 4000 years, mostly by farmers and fishermen, until it was finally abandoned in the 17th century.

We follow her around excavated stone ruins from different epochs, including a Bronze Age smithy workshop and an Iron Age broch (roundhouse). There are traces too of a Pictish wheelhouse and a medieval Viking longhouse, plus the eerie remains of a fortified manor house built later by the Stewart earls (relatives of the monarchs who ruled Scotland and England).

It was the esteemed writer, Sir Walter Scott, who gave this property the title Jarlshof in his 1821 novel, The Pirate. Meaning "Earl's House" in old Norse, the name stuck, enveloping the wider site. When Scott came, most of the other relics were still buried in sand. Violent winter storms exposed them in the 1890s, prompting a flurry of archaeological digs.

From Jarlshof, we can glimpse Sumburgh Head, a dramatic headland at Mainland's southern tip. It's capped by a clifftop lighthouse designed by Robert Stevenson - the grandfather of another great Scottish author, Robert Louis Stevenson. At the visitor centre here, we learn that the lighthouse's radar station proved vital for Allied naval fleets and pilots in World War II. Then we peer down below, looking out for whales and dolphins in the churning waves and for noisy breeding seabirds, like fulmars, guillemots and Atlantic puffins, in the jagged cliffs.

Back in Scalloway, we bid farewell to Gill, re-embark our ship and sail 35 kilometres west to Foula. The most isolated - and probably most windswept - of the Shetland islands promises even better birding (it's a colony for an estimated 250,000 birds and its name derives from the old Norse for "Bird Island"). Foula also has us time travelling some more, as it still adheres to a version of the Julian calendar, having declined to adopt the Gregorian calendar like the rest of the UK in 1752. It essentially means they're lagging about a dozen days behind everyone else.

We discover this - and more quirks about island life - with Penny Grear, one of Foula's 35 permanent residents. She leads us on a lovely hike across the peat bogs, sharing eyebrow-raising stories and pointing out the island's post office, wool shop and primary school (it currently has five pupils). We also encounter the wildlife, spying seals snoozing by the harbour, sheep snacking on wildflower-tufted grass and, through our binoculars, ridiculously cute puffins nesting on cliff faces and sea stacks.

Cutest of all, though, are the Shetland ponies who trot towards us, sparking "oohs" and "aaahs" from our group. Most endearing is the foal with the blonde mane flowing in the breeze. He's so doe-eyed and so strokable that he'd (possibly) melt the hearts of even the villains in Shetland.