This is quality piffle, right here. It’s a short volume, and perhaps better in concept than actually in execution, at least as something to read straight through. It assembles a bunch of stories that Sayers and her correspondents came up with, explaining Peter’s family and where exactly he came from. It untangles some inconsistencies, and basically rationalises everything.
A nice thing for a collector of Sayers’ work to have, and for a major fan of Lord Peter, but perhaps not the most entertaining just to sit and read.