In this first episode the team embark on an extraordinary circular tour of the Irish Sea to visit every country and territory within the United Kingdom. The hub for this wheel around the heart of the British Isles is the Isle of Man where Neil Oliver explores the small island. On the edge of the Irish Sea at Morecambe Bay, Alice Roberts gets trapped in quicksand to discover why it is so sticky and so deadly. In Northern Ireland, Miranda Krestovnikoff sees how seals cope with the struggle to find food as they bring up pups in the beautiful inland sea of Strangford Lough. Nick Crane goes sea cliff climbing on the remarkable rocks of Anglesey as he explores why this corner of North Wales is the site of some of Britain's biggest earthquakes.