This 1999 novel by Iain Pears relates the strange events in and around Oxford in 1663. It mixes fictional characters with historical personalities against the backdrop of the first few years of the return of monarchy after Oliver Cromwell's Protectorate. It starts simply enough, with the tale of Marco De Cola, younger son of a Venetian merchant, a dilettante, wandering Europe studying philosophy and medicine. He falls in with Richard Lower, treats an old woman for a broken leg, and gets tied up in a murder trial. He and Lower invent blood transfusion to treat the old woman, mother of servant girl Sarah Blundy, who is impugned as a harlot, tried, and executed for the murder-by-poison of an Oxford Fellow. Her body is butchered in a ham-handed dissection, and De Cola leaves for the continent, writing his story years later out of ire that his discovery of how to transfuse blood has been attributed to others.

But wait. There's more.

The second part of the book tells the same time, the same events, but from the perspective of a young man trying to regain the honor of his family. This deluded scion rapes Sarah, frames her for murder, nearly kills a man because he mistakes him for the devil, and in general screws up everything he touches.

But wait. There's more.

The third part of the book is told by Dr. John Wallis, mathemetician and cryptographer, who is looking for the key to some encrypted letters. Wallis knows something -- he knows the truth about De Cola. Perfumed, plump, peripatetic Marco De Cola is an assassin, sent to England with one thing in mind, murder. He knows that Sarah did not kill the professor. It was De Cola.

But wait. There's more. The fingerpost of the title is from Bacon, and refers to the objective observer, with a reputation of honesty and no axe to grind.

Enter Anthony Á Wood, Oxfordian, historian, wallflower, and the only man who knows the whole story. You see, not only was he Sarah's lover, but he quite inadvertantly killed the professor. He knows the real secret of Marco De Cola and his mission in England.

Cometh The Spoiler
De Cola is really the older sibling, Andreas De Cola, a Catholic priest sent to England to baptize the king. Charles II was the secret Catholic monarch of a Protestant country. Sarah Blundy was not executed and butchered -- she survived being hung, and the violated corpse presented to the court was a pauper woman who had died naturally, and been sold for the express purpose of anotamical research. Blundy was innocent of the charges leveled against her -- but she was a heretic. Jack Prescott is insane, and wrote his chink of the four-part memoir from Bedlam.