Two reasons for this rating:

1) It's sooooo slowwww. It's fun for the whole focus to be on Russell and I do enjoy a lot of her wandering about, but slightly less of it would be much better. I forgot that this one has always been one of my least favorites of the series (though maybe I'll revise that during my reread).

2) I knew this is the one where marriage becomes a thing, but it's been years since I read this book and in the others I sort of treat the marriage as a historical convenience. Annoying for lots of reasons, but convenient for legal and social reasons. But this time around I'm super creeped out by the way Russell describes her feelings for Holmes (and the way Holmes talks about Russell at the end). I think in the past I'd basically either missed, blotted out, or not had the same issues with those details (I was much, much younger - early twenties - and my awareness of things like grooming was much lower). In the end, I'll probably write the romance bits of this off as being an odd plot aside (it's less than 10% of the book) and keep headcannoning the marriage as a convenience for the characters and the author.