It’s 1820 and nineteen-year-old Mercy arrives in London. Orphaned as a child, she has come to live with the well-to-do Dr Stephens and his wife, Catherine, a passionate campaigner for the abolition of slavery. Mercy has never questioned her background, but the exhibition of Gericault’s The Raft of the Medusa brings confusing memories to the surface: the creaking of wood and the splash of sea-spray.

Meanwhile, Mat, a young black sailor has arrived in the city. Having been separated from his little sister fifteen years ago when they were both sold into slavery, Mat now has one mission in mind: to find the men responsible, and to take his revenge. When he discovers that his sister is still alive and living in London he is overjoyed but he soon realises that she could be in grave danger.

As dark clouds gather, the siblings must discover the truth about Mercy’s past, and find a way back to each other, before it’s too late.