September 1878. One night, as the pleasure boat the Princess Alice makes her daily trip up the Thames, she collides with the Bywell Castle, a huge iron-hulled collier. The Princess Alice shears apart, throwing all 600 passengers into the river; only 130 survive. It is the worst maritime disaster London has ever seen, and early clues point to sabotage by the Irish Republican Brotherhood, who believe in restoring Irish Home Rule. For Scotland Yard Inspector Michael Corravan, born in Ireland and adopted by the Irish Doyle family, the case presents a challenge he must struggle to face.