The thing I always tell my writing students - I'm not a full-time instructor, by any means, but periodically I've taught writing students - what I always tell them is that the most important thing in narrative nonfiction is that you not only have to have all the research; you have to have about 100% more than you need.
I was once again looking for a book idea, and I remembered Holmes, but I specifically remembered that there was this World's Fair thing in the background. I thought, 'I'll read about the fair.' I had nothing better to do. I'd dismissed about a dozen ideas, and I was getting sort of antsy. I started reading, and that's where I got hooked.
What drove me to do 'Dead Wake' was that after doing the most preliminary of reading and scoping out what kinds of materials might be available in archives and so forth, I realized that this book - the research, the writing - would present me with a rare opportunity to explore to a full extent the potential for suspense in a nonfiction work.