1679. A year has passed since the sensational attempt to murder King Charles II. London is still inflamed by fears of Catholic plots. Harry Hunt--estranged from his mentor Robert Hooke and no longer employed by the Royal Society--meets Sir Jonas Moore, the King's Surveyor-General of the Board of Ordnance, in the remote and windswept marshes of Norfolk. There, workers draining the fenland have uncovered a skeleton.

Accompanied by his friend Colonel Fields, an old soldier for Parliament, and Hooke's niece, Grace, Harry confirms Sir Jonas's suspicion: the body is that of a dwarf, Captain Jeffrey Hudson, once famously given to Queen Henrietta Maria in a pie. During the Civil Wars, Hudson accompanied the Queen to France to sell the Royal Jewels to fund her husband's army. He was sent home in disgrace after shooting a man in a duel.

But nobody knew Hudson was dead. Another man, working as a spy, has lived as him since his murder. Now, this impostor has disappeared, taking vital information with him. Sir Jonas orders Harry to find him.

With the help of clues left in a book, a flying man, and a crossdressing swordswoman, Harry's search takes him to Paris, another city bedeviled by conspiracies and intrigues. He navigates its salons and libraries, and learns of a terrible plot against the current Queen of England, Catherine of Bragan a, and her gathering of Catholics in London. Assassins plan to poison them all.

The Poison Machine is a nail-biting and brilliantly imagined historical thriller that will delight readers of its critically acclaimed predecessor The Bloodless Boy.