The book plays very strongly into the idea that mental instability and genius are two sides of the same coin by contrasting James Murray, the largely self-taught philologist and lexicographer who was the primary editor of the OED with William Chester Minor, a brilliant, mentally ill surgeon who became a valuable and prolific contributor to the creation of the OED. Winchester implies that the meticulous and intense nature of the work of producing the OED has something in common with the obsessive thoughts of paranoid delusions.

Some recent research has found some links between high levels of creativity and a propensity toward mental illnesses such as depression and psychosis. Minor’s intellect and creativity—particularly his astonishing accuracy and eye for detail—were hallmarks in his contributions to the OED, which were far superior to those of other contributors.

Nevertheless, Minor suffered from profound mental illness. His condition proved confusing to psychiatrists because of the almost unfathomable contradiction of his lucidity and his paranoid delusions. Throughout his time at Broadmoor, Minor was certain that his persecutors were breaking into his room at night to do unspeakable things to him. Yet, he filled his cell with scholarly literature, and supplies for his artistic pursuits of painting and music.