In a room with no windows on the eastern coast of Africa, an Englishman, James More, is held captive by jihadist fighters. Posing as a water engineer to spy on al-Qaeda activity in the area, he now faces extreme privation, mock executions and forced marches through arid Somali badlands. Thousands of miles away on the Greenland Sea, Danielle Flinders, a biomathematician, prepares for a dive to the ocean floor to determine the extent and forms of life in the deep.

Both are drawn back, in their thoughts, to the Christmas of the previous year, and to a French hotel on the Atlantic coast, where a chance encounter on the beach led to an intense and enduring romance, now stretching across continents. For James, a descendant of Thomas More, his mind escapes to utopias, and fragments of his life and learning before his incarceration, now haunting him. Danny is drawn back to mythical and scientific origins and to the ocean: immense and otherworldly, a comfort and a threat.

Submergence is a love story, a meditation on mortality, and a vivid portrayal of man's place on Earth. With it J. M. Ledgard proves himself a writer of large horizons and vast ambition.