Twenty years after the murder of her fathera member of parliamentand her mothers conviction for the crime, Fiona Cartwright returns to Ireland to prove her mothers innocence. Fiona struggles through the morass of clues she hopes will lead to the assassin. She thwarts the family barrister, Sir Dylan Kerrigan, immersed in a treacherous plot to fund the IRA's plan to bomb the London Tower Bridge.Possessed by her need to solve the case, she enters the secret society of the Shamrock Brotherhood, an organization long part of her father's secret life as a double agent. Her childhood nanny, Erinwhose lapse of memory has prevented the solving of the case, is treated with a drug that finally loosens her tongue. The answers are almost in place, but with the tragedy of her mother's death, Fiona falls over the edge into drunkenness and despair. Not until an unexpected accident knocks her unconscious is she transported back to the night of the murder, and discovers the identity of the assassin.