Matthew Bartholomew, unorthodox but effective physician to Michaelhouse college in medieval Cambridge, is as worried as anyone about the pestilence that is ravaging Europe and seems to be approaching England. But he is distracted by the sudden and inexplicable death of the Master of Michaelhouse - a death the University authorities do not want investigated.

Easter, 1177. Canterbury Cathedral, home to the tomb of martyr Saint Thomas Becket, bears the wounds of a terrible fire. Benedict, prior of the great church, leads its rebuilding. But horror interrupts the work. One of the stonemasons is found viciously murdered, the dead man’s face disfigured by a shocking wound. When the king’s clerk Aelred Barling and his assistant Hugo Stanton arrive on pilgrimage to the tomb, the prior orders them to investigate the unholy crime.

London in the spring of 1665 is a city full of fear. There is plague in the stews of St Giles, the Dutch fleet is preparing to invade, and a banking crisis threatens to leave Charles II's government with no means of paying for the nation's defence. Amid the tension, Thomas Chaloner is ordered to investigate the murder of Dick Wheler, one of the few goldsmith-bankers to have survived the losses that have driven others to bankruptcy - or worse.

Hugh of Singleton, fourth son of a minor knight, has been educated as a clerk, usually a prelude to taking holy orders. However, feeling no certain calling despite a lively faith, he turns to the profession of surgeon, training in Paris and then hanging out his sign in Oxford. A local lord asks him to track the killer of a young woman whose bones have been found in the castle cesspit. She is identified as the impetuous missing daughter of a local blacksmith, and her young man, whom she had provoked very publicly, is in due course arrested and sentenced at the Oxford assizes.

As the leading churchmen and women gather at the Synod of Whitby in AD 664 to debate the rival merits of the Celtic and Roman Churches, tempers begin to fray. Conspirators plot an assassination, while mysterious, violent death stalks the shadowy cloisters of the Abbey of St Hilda. When the Abbess Etain, a leading speaker for the Celtic Church, is found murdered, suspicion inevitably rests on the Roman faction. Attending the Synod is Fidelma, of the community of St Brigid of Kildare.

October, 1604. Former ship's surgeon turned country physician Gabriel Taverner is surprised to receive an urgent summons from his old naval captain. Now docked in Plymouth harbour, having recently returned from the Caribbean, Captain Colt believes his ship is haunted by an evil spirit and has asked Gabriel to investigate. Dismissive of the crew's wild talk of mysterious blue-skinned ghosts, Gabriel is convinced there must be a rational explanation behind the mass hallucinations.

At the May Day dancing at Glasgow Cross, Gil Cunningham sees not only the woman who is going to be murdered, but her murderer as well. Gil is a recently qualified lawyer whose family still expect him to enter the priesthood. When he finds the body of a young woman in the new building at Glasgow Cathedral he is asked to investigate, and identifies the corpse as the runaway wife of cruel, unpleasant nobleman John Semphill. With the help of Maistre Pierre, the French master-mason, Gil must ask questions and seek a murderer in the heart of the city.

LONDON, 1590. Queen Elizabeth I's control over her kingdom is wavering. Amidst a tumultuous backdrop of Spanish plotters, Catholic heretics and foreign wars threatening the country's fragile stability, the body of a small boy is found in the City of London, with strange marks that no one can explain. When idealistic physician Nicholas Shelby finds another body displaying the same marks only days later, he becomes convinced that a killer is at work, preying on the weak and destitute of London.  

It's 1194, and Sir Faucon de Ramis, the shire's newly appointed keeper of the pleas, must do his duty and make an official declaration of the cause of a miller's death. Saddled with a clerk who names Faucon his "penance", the shire's first crowner must thread the tangled relationships between the sheriff, the village of Priors Holston, and the priory that once ruled it. As a simple task takes a turn to the political, what seems obvious isn't, and what appears safe turns out to be more dangerous than he could imagine. 

England, 1176. Aelred Barling, esteemed clerk to the justices of King Henry II, is dispatched from the royal court with his young assistant, Hugo Stanton, to investigate a brutal murder in a village outside York. The case appears straightforward. A suspect is under lock and key in the local prison, and the angry villagers are demanding swift justice. But when more bodies are discovered, certainty turns to doubt - and amid the chaos it becomes clear that nobody is above suspicion.