A forthcoming book revealed that presumptive Democratic nominee Hillary Clinton apparently once threw a Bible at the back of a Secret Service agent.

The book "Crisis in Character" is authored by former Secret Service agent Gary Byrne, who said he was detailed at the White House for eight years in the 1990s during the time of President Bill Clinton.

"The First Lady had a different sort of liveliness," Byrne writes in the book, according to Breitbart News. "She once threw a Bible at an agent on her detail, hitting him in the back of the head. He bluntly let her know it wasn't acceptable. He told me that story himself."

Byrne says for Secret Service agents, a detail to Hillary "was a form of punishment handed down by passive-aggressive middle management."

He claims that Clinton exhibited a pattern of mad behaviour as she "vented on everyone" and "it got worse."

"Most of us knew how to brace for her inevitable eruptions. They didn't happen every day, but behind closed doors we learned about them fast. In public, she was everyone's best friend. Privately, she was her normal self," he writes in the book.

He says one time, Clinton told a Secret Service agent to "Go to hell!"

A new officer once said, "Hey you'll never believe it, but I passed the First lady and she told me to go to hell!"

After the incident, the Secret Service agent, he says, "circulated a memo reminding everyone to report any 'unusual' First Family interaction to their supervisors."

In another excerpt, Byrne recounts an episode where Hillary told her husband that the Secret Service was out to get them.

"'They f—ed us, Bill!' Hillary screamed. I stifled a laugh. The president tried his best to calm her down. He couldn't. Hillary Clinton possessed no perspective. 'We need to get rid of these assholes, Bill!' She thought she was being tough—in command—but the issue commanded her. She fumed that the Secret Service's Uniformed Division, my branch, disloyal leftovers from Papa Bush, conspired against the administration. 'They've had it out for us from the beginning!' she kept yelling," Byrne writes in the book.

"Hillary's antics made my job interesting," Byrne says. "She'd explode in my face without reservation or decorum..."

The book will come out on Tuesday.

Byrne has a 29-year career in law enforcement and enlisted in the U.S. Air Force in 1982. He became part of the Air Force Security Police. Among his awards include Good Conduct Medal, the Air Force Longevity Service Award Ribbon and the AF Small Arms Expert Marksmanship Ribbon.

He was detailed at the White House as a U.S. Secret Service Officer in 1991 and served until 1998 near the end of the Clinton administration.

Secret Service veterans denounced his memoirs, saying "There is no place for any self-moralizing narratives, particularly those with an underlying motive," according to Politico.