Gallagher’s unusual sleuth, Sebastian Becker, special investigator to the lord chancellor’s visitor in lunacy, must determine an arsonist’s sanity in The Authentic William James (Subterranean; pub month, Sept.; Reviews, July 4).

Was there an actual special investigator to the lord chancellor’s visitor in lunacy?

The visitor in lunacy was a genuine post, but his special investigator is my own invention. I based the notion on those law firms that employ former police officers to do their legwork. The visitor’s job was to interview any person of means with mental-health issues to assess whether they were competent to manage their own finances. Those found unfit could have their affairs taken over by the Masters of Lunacy, who were lawyers appointed to control your money and property. You can imagine how popular they were. The underlying intention was benign, but it created a strong incentive to conceal mental illness and to cover up its consequences.

The system seems susceptible to abuse.

Yes, there was a flip side to it as well, where people would try to get vulnerable relatives declared insane in order to get hold of their property. The 19th century saw the rise of “the mad-doctor” who’d be willing to diagnose your rich spinster aunt or eccentric uncle in return for a fee.

The plot involves a Wild West act—why were they so popular in England?

William Cody brought Buffalo Bill’s Wild West to England on three separate occasions and was feted wherever he went. Queen Victoria was a fan. When Cody’s company left for the last time, there was a void that local people rushed to fill. Homegrown sideshow acts sprang up and toured with traveling fairs. With Buffalo Bill safely out of the country, most could get away with claiming a personal acquaintance and to have toured along with him. Some even claimed to be the actual Buffalo Bill. The starting point for The Authentic William James was my wondering what kind of scenario might lead a British sideshow cowboy to have to play the hero for real.

What sources did you use on the treatment of mental illness in the early 20th century?

Mostly, I rely on case histories and firsthand accounts, primary sources where you don’t only get the information, you get the unfiltered attitudes of the time. I’ll look at hospital floor plans and patient photographs, which really can be worth a thousand words. The collected histories of criminally insane inmates are available in scanned e-book form. For context and social detail, I’ll go to gazetteers and travelers’ handbooks, anything where I can be 100% certain that everything I’m looking at is contemporary and within date. For The Authentic William James, it was mostly American hometown newspapers of 1913.