In 1864, Antoni Riubò enlists as a doctor on board the brig Verge de Montserrat, a commercial ship making the crossing between Barcelona and the Americas, by way of Africa. When he gets to Sierra Leona, the young doctor discovers that the ship is ruled by a slave trader who is taking advantage of the voyage to take hundreds of Africans to America and sell them into slavery on the plantations. Scandalised at this discovery, the doctor comes up with various ways of sabotaging the slavers' plans.