The floppy disk where Petina Gappah saved early drafts of her historical-fiction novel “Out of Darkness, Shining Light” now serves as a lucky charm, 21 years after she began.

It took that long because the story she wanted to tell was a complex one: that of the arduous, nine-month journey in 1873 of 69 workers as they transported the body of the explorer David Livingstone from the interior of Africa to the coast of Zanzibar, where he was carried to Britain for burial. It took so much research that Gappah, 48, finished and published three other books over the time she worked on it, while navigating a career as an international trade lawyer in Geneva.

She scoured book fairs and museums, acquiring a first edition of Henry M. Stanley’s “How I Found Livingstone,” as well as other “Livingstonia” related to the man, who died in what is now Zambia as he searched for the source of the Nile. “I remember at one time spending something like $4,000 for a huge collection of stuff,” Gappah said. “I had to not eat lunch for three months.”