Enzo Macleod gave up a career as a brilliant forensic biologist to follow his lover to France. Now a lecturer at the University of Toulouse, and single again following his lover’s death in childbirth, his interest in forensics is re-ignited when he is given a book about the seven most celebrated unsolved French murders of recent times.

He is convinced that by applying the latest forensic techniques, it should be possible to solve cases where the trail has long gone cold and, joining forces with the author of the book, Roger Raffin, whose wife’s murder is one of the cases explored in the book, he sets out to investigate the mysterious disappearance, years earlier, of Jacques Gaillard, one of the most powerful Civil Servants in France, whose body has never been found. A curious final entry in Gaillard’s diary, and a DNA profile from a hair found in his old apartment, lead Enzo and Raffin to a gruesome discovery and they find themselves following a trail of increasingly cryptic clues to his fate, a trail which culminates in a deadly confrontation in the dark catacombs beneath the streets of Paris.