The story is of Dick Sands - a 15 year old crew member on a ship with an eclectic collection of people on board during this particular voyage. After a tragedy, he is left to run the ship himself. They eventually run ashore and (thinking they are in South America) meet a man called Harris, who generously offers to be their guide in getting back to "civilisation." However, he has more sinister plans, as it turns out they are actually in Equatorial Africa at the height of the slave trade. Capitalising on their delusion, Harris betrays them and the party is enslaved. The rest of the book is an account of their (especially Dick's) attempts at resistance and escape.