What drives someone to commit the unthinkable? Paul E. Mullen, one of the world's pre-eminent forensic psychiatrists, examines the complex workings of the lone multiple murderer - a spectre haunting modern societies. With unflinching clarity, Mullen draws on his decades assessing massacre perpetrators first-hand, bringing readers into a dark landscape populated both by killers who attained the ugly fame they had sought as well as lesser-known but equally chilling cases. Mullen illuminates the troubling patterns that unite these murderers, such as obsessive rage; personal grievance; fascination with weapons; and yearning for infamy. Their actions are ultimately rooted in their desire for personal destruction, often culminating in suicide. He also considers the impact of media sensationalism on the killers' grandiose fantasies, often inspiring copycat violence, and proposes steps toward better threat assessment and identification of warning signs. Challengingmyths around madness and violence, Mullen reveals the unsettling truth: lone mass killers are not incomprehensible monsters, but deeply disturbed people shaped by knowable forces that, when properly understood, can be countered effectively.