Sebastian St. Cyr thought a notorious killer had been brought to justice until a shocking series of gruesome new murders stuns the city in this thrilling historical mystery from the  USA Today  bestselling author of  Who Speaks for the Damned . It's October 1814. The war with France is finally over and Europe's diplomats are convening in Vienna for a conference that will put their world back together. With peace finally at hand, London suddenly finds itself in the grip of a series of heinous murders eerily similar to the Ratcliffe Highway murders of three years before.  In 1811, two entire families were viciously murdered in their homes. A suspect--a young seaman named John Williams--was arrested. But before he could be brought to trial, Williams hanged himself in his cell. The murders ceased, and London slowly began to breathe easier. But when the lead investigator, Sir Edwin Pym, is killed in the same brutal way three years later and others possibly connected to the original case meet violent ends, the city is paralyzed with terror once more.  Was the wrong man arrested for the murders? Bow Street magistrate Sir Henry Lovejoy turns to his friend Sebastian St. Cyr, Viscount Devlin, for assistance. Pym's colleagues are convinced his manner of death is a coincidence, but Sebastian has his doubts. The more he looks into the three-year-old murders, the more certain he becomes that the hapless John Williams was not the real killer. Which begs the question--who was and why are they dead set on killing again? Praise for What the Devil Knows "What the Devil Knows  shows C.S. Harris at her best. Tightly plotted, fast-paced and based on historical events, the 16th entry in the Sebastian St. Cyr series brings the seamy side of Regency life to light.”--Shelf Awareness  “An intricate puzzle, based on a series of real-life murders, that indicts social injustices that continue to this day.”-- Kirkus “Excellent…Harris makes good use of the available evidence concerning the historical crimes, crafting a clever and suspenseful plot. Fans of David Morrell’s  Murder as a Fine Art  will be pleased.”-- Publishers Weekly , Starred Review “As readers try to guess the identity of the killer, they will enjoy the ride through the many levels of Regency English society this case involves.”-- Booklist C. S. Harris is the USA Today bestselling author of more than twenty-five novels, including the Sebastian St. Cyr mystery series; as C. S. Graham, a thriller series coauthored by former intelligence officer Steven Harris; and seven award-winning historical romances written under the name Candice Proctor. Chapter 1   Saturday, 8 October 1814   Molly Maguire hated the fog. Hated the way it reeked of coal smoke and tore at her throat. Hated the way the damp, suffocating blanket could turn even the most familiar lane into something ghostly and strange.   It was always worse at night, when the temperature plummeted and folks lit their fires. That's when the mist would drift up from the docks, swallowing the dark hulls and tall masts of the big ships at anchor out on the river and creeping along the mean streets and foul alleyways of the part of East London known as Wapping. Sometimes Molly would dream of a different life, the life she'd once known, when cold, wet nights were spent safe and dry in a warm, gently lit cottage. But that life belonged to the past. In this life Molly walked the streets at night.   She'd been on her own since before she turned thirteen, and she told herself she should be used to it by now. Yet after three years, she still shrank from servicing men with foul breath and rough hands and urgent, rutting manparts. It didn't hurt anymore like it had at first, at least not usually. But Molly still hated it even more than she hated the fog.   The bell in the clock tower of St. George's-in-the-East struck midnight, the dull clangs sounding oddly loud in the dense fog. If business had been good, Molly would have given up and gone back to the small, wretched room she shared with five other girls. But she was desperate for money. It might be Saturday night, but the fog had driven most potential customers off the streets. She'd had a couple of drunken seamen who took turns on her, one right after the other, then demanded a discount. But even they weren't as bad as the fat old magistrate who'd pinned her against one of the looming towers of St. George's.   A man like him, he could've bought himself a fine piece of Haymarket ware and tumbled her in the back room of a Covent Garden coffeehouse. Instead he'd picked up a cheap little Wapping doxy and taken her up against the soot-stained old stones of the church, his big hands tearing at her bodice and painfully squeezing her breasts as he thrust into her hard enough to make her wince. She could still smell the stink of his spilled snuff and fine brandy clinging to her. And when it was all over and she'd asked for her money, he'd laughed at her.   "I don't pay whor