No doubt I will not be the last to remark that this is the most fascinating book Patrick McGrath did not write. It has all the ingredients of one of McGrath’s icily stylish novels: madness, violence, arcane obsessions, weird learning, ghastly comedy, all set out in an atmosphere of po-faced, high neo-Gothic. The geographical span is wide, from Dickensian London to Florida’s Pensacola Bay, from the beaches at Trincomalee to the Civil War battlefields of the United States. The main characters are a pair of Victorian gentlemen, learned, serious, highly respectable, remarkable only in that one of them is a lexicographer of genius, the other a madman and a murderer.

The story was already known. The journalist and author Simon Winchester first came across it, he tells us, in Jonathan Green’s 1996 study, Chasing the Sun: Dictionary Makers and the Dictionaries They Made, which sent him on to Caught in the Web of Words, a biography of James Murray, the