Beautiful and mysterious student Marion Summers goes into a seizure at the Reading Room of the London Library, slips into a coma, and dies shortly thereafter. The autopsy reveals the cause as acute arsenic poisoning -- and there's no reason for Summers to have been exposed to this once-common, now-rare poison. With the help of her superior, DCI David Brock, newly promoted DI Kathy Kolla of the Serious Crime Unit of Scotland Yard investigates.