England, 1897. London is preparing for Victoria's Diamond Jubilee, the celebration to mark her sixtieth year as queen and empress of a quarter of the surface of the globe. Fifty thousand troops from across her vast empire will gather in the capital — and the immense importance of the occasion inevitably brings danger in its wake.

The troubles begin when a body is found floating in the Thames at London Bridge. Scotland Yard calls in Lord Francis Powerscourt, whose investigation leads him to a mysterious mansion in Oxfordshire with ancient temples in its gardens and more recent secrets in the house. There a second corpse is found, burned to death, in a room locked from the outside. Following the deaths by water and fire, Powerscourt is led into the arcane world of bonds and futures in the City of London, before a cryptic message from an old friend takes him back to his native Ireland and a terrifying night encounter deep in the Wicklow Mountains. Powerscourt's own life, and that of his family, are in terrible danger unless he can crack the riddle of the Jubilee.