As an adventurer, wilderness expert and chief scout, Bear Grylls has travelled to some of the most hostile environments in the world, sharing his survival secrets with audiences of millions. Bear is curious about a tendency to ‘follow the path less trodden' so he's now embarking on a journey into his family's history. The trail starts at home where, alongside his wife Shara, Bear explores his paternal grandfather Ted Grylls's old trunk, intriguingly full of documents marked ‘Top Secret'!

Bear heads to Sandhurst Military Academy where his grandfather Ted trained to be an army officer in the 1920s. Here Bear discovers Ted's fascination with all things mechanical – especially tanks. With help from the team at the British Tank Museum, Bear learns how Ted became one of the British Army's biggest experts in armoured vehicles and tank warfare, advising both the British and Americans on how to win on the battlefield and contributing to the success of the D-Day landings.

But it's Ted's job leading top secret organisation T-Force that helps Bear really understand the pressures his grandfather faced and reveal clues about his character. Charged with identifying, tracing and sometimes even kidnapping Germany's best scientists for interrogation by the Allies after the war, Ted had to stay in Europe long after World War II was over, working on a morally complex mission, far from his family.

Bear also wants to find out more about the life of his beloved, ‘bear hug of a man', grandad Neville. Neville's father and Bear's great-grandfather, Lionel Ford, is revealed to be a loving family man and progressive headmaster who modernised Harrow School. In Harrow's Headmaster's House, where his grandad played as a boy, Bear discovers the truth behind a family tragedy – the death of his great uncle Richard, who died of an infection as a teenager. As a father of three boys himself, Bear is moved to read Lionel's own words about his grief and love for a lost son.

Finally, following his family line back several centuries reveals, to Bear's delight, Scottish ancestry. His habit of walking the dog in a kilt no longer feels fraudulent! A trip to Scotland uncovers the story of Bear's ten-times great-grandfather the Duke of Argyll, whose religious beliefs and devotion to Scotland cost him his head, courtesy of the Scottish maiden, a gruesome type of guillotine. And at his last destination, his mum's dreams of a royal connection come true. At the Argyll Mausoleum, Bear discovers his 21-times great-grandfather is none other than a famous Scottish king.

Doctors Chris and Xand van Tulleken are identical twins, medical doctors and science broadcasters. They grew up in London, surrounded by old paintings and documents commemorating a host of characters from their Dutch ancestry. But despite the wealth of the family archive, the twins know very little about their Dutch family history, except how to pronounce their surname correctly and rumours of a connection to Dutch nobility.

A chat with mum and dad provides some intriguing clues, a coat of arms that no-one can translate, a silver shovel that hints at an Indonesian connection and a document about a Dutch sea captain with links to the British Navy. Keen to find out the family stories behind all these familiar but mysterious artefacts, Chris and Xand start with sea captain Jan Tulleken and head to Chatham Docks.

They soon uncover the eventful seafaring career of their four-times great-grandfather Jan Tulleken, a staunch royalist who joined the Dutch navy at 13 and, as war engulfed the Netherlands, was exiled in England alongside his leader, the prince of Orange.

Chris and Xand follow the trail of Jan back to the Netherlands, where they discover how Jan was tasked to protect Dutch trade routes against Algerian pirates – a mission that ended in failure. Undaunted by his tarnished reputation, Jan applied for noble status. Excited to finally get to the bottom of their noble roots, a trip to The Hague's Supreme Council of Nobility brings Chris and Xand firmly back down to earth.

By following Jan's line further back, the twins uncover a letter that reveals an Ambrosius Tulleken, Jan's father and the twins' five-times great-grandfather, who died in Demerara (now Guyana,) which at the time was a Dutch colony. Following this lead reveals a troubling story.

The twins also believe there is a family connection with Indonesia and taking the silver shovel to an expert reveals the story of their three-times great-grandfather Hendrik de Bruijn, a Dutch engineer working on canals in Indonesia who married Maria de la Brethoniere, the daughter of a French coffee baron and an Indonesian woman. Chris and Xand have confirmed their Indonesian heritage and as they learn more about their three-times great-grandparents, the twins are moved to read a document that recounts Hendrik's profound grief after his wife's death, suggesting that this was a marriage of deep love.

For Chris and Xand, it's a journey that has changed them forever, as they've found answers about their name and their heritage that were previously unknown and entirely unexpected.