Basically an Ace Doubles of interlinked stories, and it's fine, quite clever, though I felt the mystery in the 1880s was more involved than that of the 1930s. If the 1880s story had been interwoven with the 1930s, I wonder if the effect would have been the same? Anyway, I suggest reading the 1880s story first as it gets referenced a lot in the 1930s story.