Seventeen-year-old Hector Lynch and his sister Elizabeth are sent every summer to study at the Franciscan friary in a small Irish village. They are snatched from their beds by Barbary corsairs and Hector is sold at auction in Algiers. He has no idea what has happened to his sister. Hector is sent for hard labour in the bagnio, where he makes a friend in Dan, a Miskito Indian from the Caribbean. Hector and Dan have individual talents - Hector is highly educated, while Dan is an artist and expert shot - and so, once they've converted to Islam, they soon find favour with their master and their way out of the bagnio. Their good fortune doesn't last, and they soon find themselves in slavery once more, this time in the French galleys. But Hector is still determined to find his sister...