February 1816: A race through the icy, twisting cobblestone streets of London ends inside an abandoned church—and a horrific discovery. Bow Street Runner Sam Kelly is called to investigate the grisly murder of Sir Giles Holbrooke, who was left naked and garroted, with his tongue cut out. Yet as perplexing as that crime is, it becomes even stranger when symbols that resemble crosses mysteriously begin to appear across the dead man's flesh during autopsy. Is it a message from the killer?

Sam turns to the one person in the kingdom who he believes can answer that question and solve the bizarre murder—the Duke of Aldridge's odd but brilliant ward, Kendra Donovan.

While Kendra has been trying to adapt to her new life in the early nineteenth century, she is eager to use her skills as a twenty-first century FBI agent again. And she will need all her investigative prowess, because Sir Giles was not an average citizen. He was one of England's most clever spymasters, whose life had been filled with intrigue and subterfuge.