London is a mad city in all senses of the word, from the Romans to Victoria to this age of Blair. It’s mad as in “exciting,” mad as in “angry,” and can definitely drive those who live in it insane. With his sixth book, Greg Hollingshead goes back to one particularly mad era of London.

It’s the late 18th century, when ripples from the French revolution are still being felt. Republicans are locked up without second thought. After all, who could be more of a lunatic than someone who wants to do away with the King? Amidst this turmoil stands – barely – the crumbling mess that is Bethlem, the famous home for the insane. In Bethlem we find James Tilly Matthews, a revolutionary who was once jailed in France and is now for some devious reason kept shackled in the asylum.

Matthews is a nutcase. He believes a gang of conspirators is always working nearby, operating a contraption called an Air Loom with the purpose of doing him harm. The Air Loom allegedly performs hideous deeds, including brain-sucking, in which a magnetic attachment vacuums the contents of his head. But there’s more to Matthews’ confinement, and these other reasons are murky and possibly political.

Standing by her man is Matthews’ wife, Margaret, whose frequent attempts to speak, visit, or even get letters to him are foiled by John Haslam, the apothecary and administrator of Bethlem. Haslam is torn between getting Matthews out of the asylum, with its bleedings, blisters, and purges, and keeping him there to study. After all, a specimen this good does not come along often. Haslam is not an evil man, just ambitious, and cares what outsiders, not insiders, think of his asylum. In his own words: “I was the one who would make of Bethlem a masterpiece that would say to the world, Here is how you order a hospital for lunatics.”

Hollingshead shuttles easily between these three points of view. It’s a dense read, but every time the novel feels weighted down by the details of madness, Hollingshead kicks the plot forward. The question remains throughout: Why is James Tilly Matthews locked away? Who is behind this?

It’s a good narrative mechanism, but Haslam’s struggles are more interesting. Here is a decent man who can’t do the decent thing, swept up in the fame of the books he publishes on Bethlem. When a visiting French doctor promises to declare him the foremost English mad doctor, Haslam can barely believe his ears. “Ah, the wonderful power of words,” he sighs. “To whisk the soul to a froth of giddy embarrassment.” And yet he knows his own fame comes at a cost to the Matthewses. “How you can think of yourself as a certain sort of person,” says Haslam near the end, “yet watch yourself behave as quite another?”

Hollingshead has done plenty of work to construct his own seamless version of historical London. The result of the days, months, years he’s spent thinking about and researching the era are, for the most part, subtly woven into the story. It’s only occasionally that a raw, undigested chunk of research appears, sticking out of the narrative, something so good that Hollingshead probably felt that he couldn’t snip it. When Haslam eats a meal at his friend’s home, we don’t just learn he’s had dessert, or that the dessert is batter pudding drizzled with four-year-old curaçao ketchup. Hollingshead gives the recipe: take half a pint of curaçao, add a pint of sherry, an ounce of lemon peel, etc. Historical novelists often have problems killing their darlings, those well-sought-out pieces of research that ultimately serve no purpose except to bog a novel down. Bedlam does bog down occasionally, but thankfully Hollingshead knows we’ll go to other books for obscure recipes or architectural detail.

Hollingshead never loses sight of his trio of characters. One finishes Bedlam not with the exhilaration of a highly charged, densely plotted political thriller – which the publishers seem to be pushing. (In the promotional bumph they make Bedlam sound like a Gene Hackman film with “shifty rules and shadowy players.”) No, it’s not that. Those looking for Murder and Mystery in Moorgate will be disappointed.

For this reviewer, the book’s pleasure came after the slog through the density, in the final chapters where the well-built, convincing 20-year history of the three characters became apparent. They’ve been bound together. All three, it seems, have dipped over and back from the line between mad and sane. Who is mad in the novel? And does being sane necessarily help one get through the turmoil of life? As Haslam himself says, “Isn’t everybody always a little bit sick? I myself have not known any person completely healthy in body and certainly never one perfectly sound in mind.”

Do not go into Bedlam expecting a cracking thriller. Madness and identity are the issues Hollingshead concerns himself with, and they make for a stronger novel than one of mere political intrigue.