The authors call Ervil LeBaron a "charismatic energumen in the tradition of Charles Manson and, more recently, the Reverend Jim Jones of Guyana fame." Indeed, it is impossible to read of LeBaron's Lambs of God without recalling those other, more widely publicized cults.

LeBaron and his Lambs, though fleetingly suspect in the assassination of John F. Kennedy, did not get much press until the 1977 murder of Dr. Rulon Allred, with which the book opens. That murder -- executed by a two-woman hit squad -- spotlighted not just LeBaron's but a number of polygamist sects. Allred had been the leader of one sect, as were two of Ervil LeBaron's brothers. Ervil, in fact, had been born to "polygs" who had fled to Mexico following their excommunication from the Mormon Church.

There is a wealth of detail about this subculture, fascinating in and of itself. More interesting, though, is the meticulous account of the way Ervil LeBaron subverted the doctrine of plural marriage to his own murderous ends.

"In a polygamist community," the authors tell us, "control of the women confers power, and Ervil understood that. Influencing them was tantamount to having a crony in every home." Thus Ervil, while still a member of his brother Joel's Church of the Firstborn of the Fulness sic of Time, organized the secret United Women of Zion. They would rid the world of his many enemies. "He said the women were going to do the killing because people weren't suspicious of women," one participant recalls. Another remembered that Ervil "really began to feel that he had God's power to go and take lives if he so desired. . . . There was a lot of talk about 'put to death, put to death.' "

LeBaron's 11th wife, Vonda, was his most willing killer, we learn in the book. Devoted to her husband, she shrugged off her "sheltered, innocent and Mormon-dominated childhood" and became a "murderess in the name of God." Vonda is said to have told another cult member of one of her crimes, "I maneuvered him over to the washbasin in the kitchen. Told him to freshen up . . . while he was washing his hands, I came up from behind and shot him three times with a .38." This to secure "her calling and election in the Kingdom of God."

Even LeBaron's male followers behave with aplomb in the face of the most grisly circumstances, the authors show us. Lloyd Sullivan, who later defected, was with Ervil LeBaron when he noticed that Ervil's Ford LTD was sagging. LeBaron had just ordered the execution of his own daughter, Rebecca. " 'I wonder if Rebecca's in the trunk,' Ervil commented idly to Lloyd, who opened the trunk about four inches and was stunned to see Rebecca Chynoweth lying there . . . obviously dead."

Several of the murders LeBaron ordered were politically inspired. His brother, Joel, is assassinated so that Ervil can assume control of Joel's Firstborn Church. When another brother, Verlan, takes over, Ervil adds Verlan to his target list. Indeed, Allred's murder was a mere convenience -- done so that Verlan would come to Allred's funeral, thus exposing himself.

More chilling is the book's account of the death of Robert Simons, who wrote Ervil asking for information about the Lambs of God. Simons got more than he bargained for: a personal visit from Ervil. When Simons refused to acknowledge Ervil as God's prophet, one of the Lambs drove Simons to the desert where two of the others were lying in wait. "Weapons drawn, they tiptoed up to within five feet of their target, who, obligingly, was standing with his back to them." The Lambs reported to their leader that Simons had been shot, doused with lime and buried. Pornographic photos in Simons' wallet later prompted "a lot of giggling. Then Ervil ordered the burning of both the wallet and Simons' jacket."

What gave Ervil LeBaron -- who had by this time declared himself the "One Mighty and Strong" -- the ability to hold others in such thrall? Would we have been able to resist? This is, of course, what powers readers through documentaries about such figures. We test ourselves. We encounter evil at a safe remove and -- whew! -- walk off whole. Every detail is thus both terrifying and reassuring.

It is never a fair test, exactly, because we meet these monsters when their madness has run its course, when they are caged, reduced. Ben Bradlee Jr. and Dale Van Atta contain LeBaron for us, as Thomas Thompson did Charles Sobhraj, as Vincent Bugliosi did Charles Manson. Crucial, though, is the illusion of test.

Here it is maintained through the steady, painstaking accumulation of fact. LeBaron rises -- and falls -- before our very eyes. This book is scholarly in its attention to even the "dim constellations around the central sun" of Ervil LeBaron.

Equally crucial is the perpetuation of threat. We quiver to think of a Charles Manson eligible for parole. Thompson leaves Sobhraj yearning to visit the United States. Bradlee and Van Atta tell us of "a hard-core dozen followers, scattered between Arizona and California. . . . The leader of this group is son Arturo LeBaron, to whom Ervil, according to prison writings police intercepted, has already passed on his mantle. At Ervil's death, Arturo becomes the "One Mighty and Strong."

In an addendum we learn that Ervil LeBaron died in his Utah State Prison cell on Aug. 16, 1981.