When it comes out next year, the still untitled volume — set in the late 1920s — will be the first new Poirot story to appear since "Curtain" was published 39 years ago.
Is the new author feeling the pressure of taking up where the world's most successful novelist left off?
Hannah, with eight popular psychological thrillers to her name, claims to be only a little bit fearful.
"The fear stroke adrenaline should help me to produce a better book," said Hannah, who's already written a 100-page plot summary complete with the twists and turns associated with Christie's style. "I'm not scared. I've done a very detailed plan that's been approved. He will certainly be the same Hercule Poirot that's in all the novels. I'm not going to give him an interest in windsurfing or scuba diving. But different aspects of his personality may come out."
Hannah said she has been a disciple of Christie since her father gave her a dog-eared copy of "The Body in the Library" when she was 12 or 13.
"I read every word she'd written within a year and I've been in love with her work ever since," Hannah said. "The main thing is her obvious love of the story and her genius as a storyteller. In the writing, you can feel her relish in the story. She tells stories that are far more imaginative and suspenseful than anyone else."
Mathew Prichard, Christie's grandson and chairman of Agatha Christie Ltd., said the decision to authorize a new "Poirot" tale was motivated in part by a belief that it would spur sales of Christie's existing works, which include 80 crime novels and short story collections and 19 plays.
"Like it or not, publishing thrives on big new titles," he said. "Although Agatha Christie books have fared remarkably well despite this trend, our publishers said if we broke our rules and had a well-known modern author do something like this, the whole list would benefit."