A novel cannot keep a secret from your right thumb. However carefully the author hides who did it, the pages under that thumb keep getting thinner, and somewhere in the last thirty you know, with no help from the plot, that it cannot be a stranger who walks in now with a limp and a motive: there isn’t room left for him to be explained. Every mystery writer is working against a reader who can count by touch. An e-book was supposed to take that away, except there is a small percentage in the corner of the screen and everybody looks at it, which is the same thumb with a number on it.