Two-hundred metres out is a line of six pontoons that stretch further and further away from land. Each has increasing amounts of cash inside and a written question with two possible answers and two corresponding hatches. Communicating with their land-based partner on arrival, the swimmer must select a hatch. If they are right, they discover cash and take it. But if they are wrong, they find a 1kg lead weight inside and must attach it to their belt.
As their partner struggles against mother nature, the team member with Rylan Clark-Neal is also desperately answering additional questions in a bid to win time because when they decide to bail, they will only win the money if they can make it back to their partner on land in time.
Overseeing their safety as the underwater currents shift, the waves change and the dense sea fog of the Atlantic descends without warning, is Olympic silver medallist and expert long distance open-water swimmer Keri-Anne Payne.
And while Keri-Anne offers tips, and Rylan offers lifelines (from surfboards to goggles, which they can exchange their cash for), ultimately the team must continually weigh up the ever-changing odds and decide when it should attempt to swim it to win it!