Victorian teachers must have had time on their hands. When Dr James Murray started work on the monumental Oxford English Dictionary, he managed to combine the task with teaching at Mill Hill public school in London, where he built a corrugated-iron scriptorium in the school grounds.

Murray used volunteers to collect quotations from 16th and 17th-century literature to illustrate the original meanings of words. The story of his relationship with William Chester Minor, the most prolific of these volunteers, is the subject of Simon Winchester’s fascinating book.

When Murray tried to meet Minor after 20 years’ collaboration by post, he was amazed to discover that his assistant was criminally insane, a resident of Broadmoor asylum. In a fit of paranoia, Minor had shot a stranger in 1872 - and spent the rest of his long life behind bars.

To tell Patient Number 742‘s story, Winchester has been allowed to delve into the Broadmoor archives. It turns out that the asylum’s longest resident had two rooms, a view of the countryside, a servant, and unlimited access to books. Although he spent his nights tortured by paranoid terrors, his days were given over to lexicography.

This book not only rescues Minor from obscurity, but also offers a neat history of English dictionaries and of the decisions that led to the OED project. In contrast to, say, French practice, the Brits decided on a descriptive rather than a prescriptive account of the language. But, being Victorians, they also saw English as God’s gift to the world and its dissemination as an imperial mission.

Murray and Minor had much in common; photographs reproduced on the endpapers show that, with their shared taste for bushy beards, they even resembled each other. Like the other hard-working obsessives who got the OED project off the ground, they had a quasi-religious commitment to language. For Minor, the work was a form of rehabilitation and redemption.

Winchester tells Minor’s strange history with a Victorian relish for lurid detail and much atmospheric colour. Wonderfully readable, full of word lore and extracts from the OED, this is a book for all who love words - and the film rights have already been sold. However, the publisher hasn’t bothered to provide an index - not a good way to commemorate either Murray or Minor.