The Woman in White
by Wilkie Collins
This thrilling novel written in 1859 and first published as a serial is considered to be one of the first mystery/detective novels ever written. The book takes the form of personal testimonies of various characters and compiled as "evidence" of a sort. It's very intriguing and compelling.
I listened to the audiobook, which used different readers for each character, making it easy to know who was "speaking." I imagine it might be a little bit difficult to keep track of the current narrator when reader it in print form. It will keep you on your toes, as will the story!