“Don’t drink the Kool-Aid.” We hear the admonition all the time, are constantly treated to the spectacle of one political pundit—or would-be pundit, anyway—accusing another of downing the fruity beverage as shorthand for uncritically following some party line or another.

But where does the expression come from? Those who were around a little shy of 40 years ago should remember well: it refers to an astonishing act of mass suicide committed by followers of a revolutionary firebrand named Jim Jones, who regarded himself as Mao Zedong one day and Jesus Christ the next, and the day in November 1978 when more than 900 of his followers in the Peoples Temple drank cyanide-laced fruit drink and died in the jungles of Guyana.

“Of course, the first thing you learn in researching the story is that it wasn’t really Kool-Aid,” Jeff Guinn, the author of the new book The Road to Jonestown: Jim Jones and the Peoples Temple, says, speaking from his home in Fort Worth, Texas. “But that doesn’t matter: we say ‘Don’t drink the Kool-Aid,’ regardless of what the drink really was. What’s more important, and what started me on this book, was when I got to thinking, ‘Here’s this expression that we use every day to say that someone is being blindly obedient to a leader or idea, and its origins are right in front of us.’ ”

If you’re of a certain age, then “Jonestown” is a byword for religious cultism gone very, very wrong. Jones himself was—well, perhaps a psychopath, perhaps a sociopath, perhaps a narcissist with a messianic complex, certainly no stranger to drugs and the pleasures of the flesh. Yet, in his time, Jones was hugely influential. When he moved his church, mostly consisting of poor African Americans, from Indiana to California, he added to his congregation a good number of well-educated, affluent whites with a commitment to social justice.

With them, his Peoples Temple became a political force, and Bay Area politicians such as Willie Brown and Joseph Alioto accepted his support and campaign contributions. Jones’ sermons rambled from here to creation, embracing the words of Buddha and Che Guevara and everyone in between, but they were compelling; as Guinn chronicles, they gave Jones the basis for bringing in atheists, drug addicts, Marxists, libertarians, Black Panthers, and anyone else who showed an interest in his cause, even as he referred to himself on the pulpit as “God, the reincarnation of Christ, or Lenin in a single turn.”

Given that his last book, Manson: The Life and Times of Charles Manson (2013), centered on another well-known psychopath, and there’s reason to worry that Guinn has been spending a little too much time on the dark side. He spent seven years writing his Jonestown book, after all, traveling in the footsteps of Jones and his followers from Indianapolis to San Francisco and the jungles of Guyana. There’s a reason for it, though: as a popular historian, Guinn sees these powerful figures as vehicles to talk in interesting ways about the chaotic times in which they lived. We all think of the present as being the worst of times, as the current headlines fearfully assure us, but looking at the ’60s through the lens of Manson or the ’70s through the lens of Jones might help readers, whether they were around that the time or not, put the headlines of today in context.

“I was thinking the other day that I’d be asked to compare the subjects of my Manson book and this new one, and what I came up with was that comparing Charles Manson to Jim Jones is like comparing Mickey Mouse to Machiavelli,” Guinn says. “There is no comparison. Manson could barely control a few teenage girls, while at his height Jim Jones had hundreds of thousands of followers all over the world.”

And whereas Manson had little to redeem him, ever, Jones was something much more than a megalomaniacal madman. “Survivors often talk among themselves about whether Jones was evil from the start or became evil later,” Guinn adds. “But it has to be said that he did a lot of good for the poor and powerless. If he’d been hit by a car before leaving Indianapolis for California, we’d remember him today as an important hero of the civil rights movement for all the work that he did in desegregating Indiana. But something happened along the way, and I think it may have been this: when you’re called God often enough, you get swept up in it, and you start to believe that maybe you are God. That’s when the trouble starts.”

The trouble started, indeed, and it ended very badly, and Guinn’s book makes for a vivid and illuminating account of a very strange episode in American history. He’s on to another strange chapter, this one involving three well-known figures who, while changing the world and making themselves immensely wealthy, just happened to invent the family road-trip vacation along the way. It’s a much happier story than the road that Guinn now takes readers on, one that is unfailingly fascinating no matter how dark.

Gregory McNamee is a contributing editor.