As ever, a beloved reread. Okay, the cypher bits can be kind of annoying unless you’re really interested in figuring out, but this time I paid close attention so I could use the Playfair cypher to write a daft message to my wife, so there’s that. I love the care Peter takes to try and be fair to Harriet, not to push her, and to do his best by her. I do think sometimes he’s rather self-pitying, but mostly his sense of humour about it alleviates that.
The mystery itself is a fun one to break: if you figure out the key to it too soon, the back and forth as Harriet, Peter and the police try to break the wrong alibis can be a bit infuriating, but it’s also pretty clever. If you don’t love Peter and Harriet (and mostly their banter), I can’t imagine it being a favourite, but for me… yeah. <3