Sean Conway is on the last leg of his attempt to complete a world first - a 4133-mile non-stop mega-triathlon around the entire coastline of mainland Britain.
Having completed a 3200-mile cycle and 818-mile run, he's been on the road for 72 days, but now faces a 115 mile swim, from Brighton, East Sussex back to his starting point in Lulworth Cove, Dorset.
This may be his toughest discipline yet; self-supported, Sean drags all his kit in a self-made raft he’s christened Rafty McRaftface. On day one he discovers it's not sea-worthy and on day 2 it disappears, presumed stolen. Reunited with Rafty (Beach Patrol took it for safe keeping) and water-tight thanks to running repairs, he tackles endless hours of swimming in the cold, energy-sapping sea of the English Channel; slaloms through the world’s busiest shipping lanes and faces off fierce tides in the unpredictable and dangerous waters of the Solent.
Finally, on the home stretch, Sean is unable to drag himself ashore due to the coastal cliffs of the Jurassic Coast, lost in sea mist, will he stamp his name in history?