The great-grandnephew of Bram Stoker is writing the first authorised prequel to Dracula, based on scholarly research into the original, unedited version of Stoker’s 1897 tale of the undead count, as well as Stoker family legends.

Dacre Stoker and co-writer JD Barker’s prequel Dracul is set in 1868, and sees a 21-year-old Bram encountering some of the creatures he would later write about. Due out next year, it has provoked great excitement in both the literary and film worlds. North American rights sold for a six-figure sum to Putnam, UK rights are with Transworld, where editor Simon Taylor called it “terrific fun – and suitably terrifying”, and film rights have gone to Paramount, where the director of the new adaptation of Stephen King’s It, Andy Muschietti, is attached to direct.

According to Dacre, who also wrote a sequel to Dracula in 2009, there are 102 pages missing from the original draft of Dracula. He believes that only 17 of them have ever been found – published as short story Dracula’s Guest by Bram’s widow Florence in 1914. Dracula’s Guest features a nameless character – “very much like” Dracula’s protagonist Jonathan Harker, said Dacre. He makes his way to Transylvania, stopping in Munich for the night. “[Florence] wrote in its preface that it was edited out of Dracula due to length,” said Dacre. “The story fits as part of the early narrative, so most likely it was part of the missing pages.”

To write their prequel, Dacre and Barker have picked over the original typescript, as well as Bram’s notes and journals, to analyse what else the lost section might have featured. They searched “for lines that were crossed out that may have referenced anything Bram had to take out of the 102 pages,” said Dacre. “These crossed-out lines gave us clues about what may have been on those missing pages. Since Dracul is a prequel … we wanted to have a really good idea what was included in Bram’s original and unedited version of Dracula.”

He describes the new book as “the story of the events in Bram’s life that led him to write Dracula … The story focuses on Bram and his family, as a young boy growing up in Clontarf, Artane and Dublin. These parts were based on Stoker family background stories [and] knowledge, all of the existing biographies, excerpts from The Lost Journal [Bram’s private notebook] and our speculation.”

But the story will centre on Bram’s encounter with “an ungodly evil, which he traps in an ancient tower”, according to the announcement of the deals for the novel in Publishers Marketplace.

Taylor at Transworld said Dracul “speculates on what Bram Stoker’s early life – he was a sickly child, often bedridden – might have been like had the creatures he later created been real”.

“The authors have very cleverly and convincingly resurrected the tone of the original but in a modernised voice,” said Taylor. “It includes some nicely handled nods to the original novel, and like Dracula often uses an epistolary narrative form. I think the novel works so well because it’s both a proper partner to the original Dracula – doesn’t mess with that story but honours it – while being a deliciously, blood-chillingly creepy horror novel in its own right.”