Summary: A while back, some important English guys came and asked Sherlock to find a stolen letter that could mean big, big war if it got in the wrong hands. It was basically an angry letter a guy from another country wrote. Sherlock had several spies as suspects, and when one turns up dead, he goes to investigate. It turns out some lied-to lover killed him because he’d been cheating on her, and the case doesn’t seem to be connected until Sherlock realizes that the important English guy’s wife had been at both scenes. He gets the wife to tell him that the spy had found the old English version of a sex tape from before she was married (a racy letter to an ex) and had threatened to go public with it unless she got him that letter. But then he was killed before he could do anything with it. Oh, and the “second stain” thing had to do with the fact that the rug at the spy’s murder scene had been moved, which was how Sherlock figured it out. And Sherlock even lets the wife keep her secret and hides the unopened letter in a bunch of other letter’s in the guy’s special document box and tricks him into thinking he was stupid and it was actually there the whole time.
I know this was long, but I also wanted to add as a side note that almost every Sherlock story is presented by Watson as “possibly the last.” From what I understand of Sir Arthur, he was sick of writing these things (though he’s seemed to have improved over time, assuming I’m reading these chronologically), so was probably hoping each one could be his last. I’m glad there still seem to be a lot more to go, though.
Sherlock Rating: 3 magnifying glasses. It was interesting, but there wasn’t much of a crime, and the only criminal involved was taken care of outside of the story.
Mystery Story Convention: Blackmail over some kind of sex-related thing, and missing/stolen government documents that could mean war.