An explosive new book claiming that the majority of Vatican clerics are gay is scheduled to be released on the same day that Pope Francis' sex abuse summit is set to begin in Vatican City.

The 570-page manuscript titled, "In the Closet of the Vatican," written by French journalist Frederick Martel, alleges that 80 percent of the priests working at the Vatican are gay, although not all are sexually active.

Martel, who spent four years researching, reveals in his book, an unspoken code with "one rule of thumb being that the more homophobic the cleric was, the more likely he was to be gay," The Guardian reported.

The book is a "startling account of corruption and hypocrisy at the heart of the Vatican," according to its publisher Bloomsbury.

What are some of the book's claims?

"In the Closet," exposes the "celibacy of priests, the condemnation of the use of contraceptives, countless cases of sexual abuse, the resignation of Benedict XVI, misogyny among the clergy, the dramatic fall in Europe of the number of vocations to the priesthood, the plotting against Pope Francis – all these issues are clouded in mystery and secrecy," Bloomsbury wrote on its website.

Martel claims that some gay priests have accepted their sexuality, while others have lived double lives while hiding their relationships with men or seeking high-risk encounters with male prostitutes. Still, others remain in denial about their homosexuality.

The book describes "a clerical culture of secrecy which starts in junior seminaries and continues right up to the Vatican itself."

However, it doesn't conflate the sexual of abuse of children with the homosexuality of the clerics.

Who did Martel interview for the book?

Martel reportedly completed 1,500 interviews with dozens of cardinals, bishops, monsignors, papal ambassadors or diplomatic officials, Swiss guards, and more than 200 priests and seminarians.

The author, who's openly gay, also spent about a week each month in Rome while conducting his research. He sometimes stayed in residences inside the Vatican or on Holy See property, according to the Catholic website, The Tablet.

What else?

The book is set to be released Feb. 21, in eight languages and across 20 countries.

The Vatican said its main aim of the summit Feb. 21-24 is to guarantee that bishops around the world "clearly understand what they need to do to prevent and combat the worldwide problem of the sexual abuse of minors."