Ross Kemp heads to north Devon to dive on the wreck of steam-age ship the Iona II, which went down on its maiden voyage to America in 1864 with a mystery cargo on board. With the help of dive supervisor Neil Brock and expert dive guide Emily Turton he pushes through intense low visibility conditions to search for an answer and finally uncovers that ship was gun smuggling for the pro-slavery Confederates during the American Civil War. The story is so shocking Ross is inspired to dive down with maritime archaeologist Mallory Haas on the site of potential early slaver ship in Plymouth. What they find underwater sheds new light on one of the most inhumane periods in British history.