Is PJ Pereira, Pereira & O'Dell's chief creative officer, the next J.K. Rowling?

Not content with winning three Grand Prix awards at the Cannes Lions festival and an Emmy for his agency's hit social-film campaigns for Intel and Toshiba, Mr. Pereira's first book "Gods of Both Worlds" is out next month. It's being described on Twitter as "Harry Potter Meets 50 Shades of Grey." In the fantasy literature genre, he explores the mythological West African gods and goddesses that inspired the controversial voodoo-like faith widely practiced in Brazil today, a topic that's fascinated PJ for years.

This potential blockbuster comes with a catch: Mr. Pereira wrote it in his native Portuguese, and next month's whirlwind book tour starts in Sao Paulo and ends in Rio de Janeiro. But his agent headed to the Frankfurt book fair this month to sell English-language rights, and he says the book has already been optioned for a possible Hollywood movie version.

The story has two sides, alternating between a young journalist in Sao Paulo and the ancient African deities. Mr. Pereira became interested in these deities, called orixas in Brazil, as a young digital creative at DM9 DDB in Sao Paulo.

"This book is my attempt to get people to respect their traditions and culture a bit more," he said. "It's about the mythology and the characters and the amazing power behind them. My intention was to tell a Harry Potter kind of story, the way J.K. Rowling created her own universe. [But] the mythology is incredibly sexual. To respect that, I had to make it sexy, too."

In a translation from the book's Portuguese-language Facebook page, the story is described: "Mythical kings, queens and warriors like Ogum, Shango, Oshosi and Iansan get together with people from today to rescue the 16 princes of fate, in a surprising and original narrative that preserves all the drama, sensuality and violence of the original myths that inspired it."

It's an action-packed book. Reading a pre-publication copy, on the first page a young female chef in a Sao Paulo restaurant is possessed by spirits in front of all the diners.

How do busy ad execs find time to write one book, let alone a whole fantasy-literature series? Mr. Pereira carved out two hours late every night, but actually wrote much of the book over four years starting a decade ago before he moved to San Francisco from Sao Paulo. He couldn't find a publisher back then who would take a chance on an unknown writer, but perseverance has paid off.

"Every day for 10 years I'd look at myself in the mirror and ask 'is today the day?' [to try again]," he said. "I had to build a name for myself first."

Mr. Pereira attributes his ultimate success in getting the book published to his better credentials a decade on, with an Emmy under his belt. Although it may also have something to do with an astute publisher eyeballing his 800-page manuscript and recommending: "Trilogy."

Slimmed down to 200 pages, the first book of what is now the "Gods of Both Worlds" trilogy (in Portuguese "Deuses de Dois Mundos") is called "The Book of Silence." It gets darker. The second, to be published in March 2014, is "The Book of Betrayal" and he's working on the third now. It's called "The Book of Death" and is already his favorite.

Drawing on his ad experience, he went to Los Angeles last week to film an elaborate trailer for the first book.