At a few minutes past noon on 15 August 1914, Frank Lloyd Wright’s mistress, Mamah Borthwick, sat down to lunch with her children, John and Martha, on the porch at Taliesin, the house-cum-atelier Wright had built for himself and his lover outside Spring Green, Wisconsin. Borthwick had left the children’s father for Wright five years before. Moments after they sat down, all three were murdered by a manservant called Julian Carlton. John was twelve and Martha nine. Having split their mother’s skull open with a shingling axe, Carlton did the same to theirs; then he turned the weapon on a tableful of Wright’s employees, killing four men and the teenage son of one of them. That done, he doused the house in petrol and burned it down. Wright was in Chicago when he was given the news.

This much, at least, is a matter of record, although other of the day’s events are far from being so. Chief among the mysteries is who Carlton was and why he did these terrible things. Those questions are central to a new study of