Piccadilly Reckoning

An explosion that rips through the elegant bustle of Mayfair. Three victims who seemingly have no connection to each other. A dangerous weapon. The glamour of Regency London explodes when a carriage carrying a former diplomat is attacked in front of a Piccadilly pub, exposing a deadly web of murder and international intrigue.
  Summoned by Bow Street, former spies Malcolm and Mélanie Rannoch rush to the scene to find the wreckage still smoldering. Sir Stephen Strangeways, who is in line for a strategic cabinet post, died in the explosion. Baron Hauke, an Austrian diplomat, and Julien Mallinson, a fellow former agent—and one of Mélanie and Malcolm's closest friends—are seriously wounded. Their lives hang in the balance while questions hang in the air.
  No one knows how the three men might be connected or who wants them dead. The search for answers sends the Rannochs deep into their past, from the scandalous history of exiled Queen Hortense Bonaparte to the dangerous intrigues of foreign revolutionaries. Julien's secrets are deeper and more deadly than even his friends know. Mélanie shares some of those secrets. Now she must reveal long buried truths that she's concealed from even her own husband. As the Rannochs race to solve the mystery and prevent a dangerous weapon from falling into the wrong hands, the safety of their country, the lives of their friends, and the future of their marriage hang in the balance...