Don't like the ending of Ken Follett's 'Pillars of the Earth'? Gamers can soon change the fate of the book's main characters in a video game adaptation of the bestseller, ready for launch in 2017.

As the sprawling medieval saga celebrates its 25th anniversary this year, Follett said it was a "fascinating experiment" to see it adapted.

"The challenge for me as a writer is to draw the reader into my imaginary world. Game is another way to do that," he said at the Frankfurt Book Fair on Thursday.

Set in 12th century Britain, the novel has sold more than 25 million copies worldwide and has already been adapted for television, said Marco Schneiders of Follett's German publisher of more than 30 years, Bastei Luebbe.

The video game would be available in versions for PC, Mac, tablet computers, Playstation and Xbox. With 25 hours of possible game time, the idea was to develop a new concept of interactive literature, Schneiders said.

Gamers can step into the shoes of one of the book's three main characters: the architect Jack; the disinherited young girl, Aliena; or the prior Philip; and make decisions that would change the direction of the story.

Compared with classical narration techniques used in novels and films, the game "adds intriguing new elements to the story, exploration of locations, interaction with the characters and the environment and decisions that players have to make," said Carsten Fichtelmann of the game's developers Daedalic Entertainment.

"We have used maybe 15 percent of original text and another 85 percent are new stories, new background stories of the characters to what already exist," he said, adding that he hoped the game would sell at least three million copies.

"All authors want constantly younger people to read their books," said Follett.

"I'm hoping that knowing that huge proportion of the playing audience is young, that the name 'The Pillars of the Earth' will become familiar to a new generation of people and maybe some of them will enjoy the game so much that" maybe they would read the book too, said the author.

If the game proves a success, Follett -- whose latest opus "Edge of Eternity" was published last year -- said he would not rule out a video game adaptation of other novels.