In Search of the Unknown. Of course, Joshi wasn't referring to the first D&D module I ever owned, Mike Carr's 1978 classic. Rather, he was talking about a 1904 book by Robert W. Chambers (of The King in Yellow fame) that's long since been in the public domain.
Seeing as I'd never heard of it before, I've never read Chambers's In Search of the Unknown, though I plan to rectify that when I have the time to do so. As I understand it, the book is actually a collection of episodic stories about a man seeking out species of animals believed extinct. This being a Chambers book, he naturally finds more than he expected.
I have no idea if Mike Carr was making a reference to this book when he named module B1. My guess is that the similarity of title is merely a coincidence, but it's intriguing nonetheless.