Allyn Gibson wrote:
The way I remember it (and it's been about fifteen years since I last read it), AaP has an opening act of about a quarter of the book where the mystery is set up. Then there are four short stories by members of the Detection Club where they swap detectives and have them offer solutions to the mystery. Then there's an epilogue where we find out the real solution to the mystery.
That's actually a little disturbing, in-story. These four great detectives, and only one of them figures out the right answer? That's a pretty low success rate, and it calls their deductions in their solo adventures into question.