The story is written really well. Lots of other people have said great stuff about it, so I get some room to criticize a bit too!
I just wonder about how you constructed the ending. It seemed like a different ending was coming in, and then the sudden <spoiler> out of nowhere is almost a diablo ex machina. It's just someone who comes out of nowhere, does one thing, and vanishes again, right at the end of the story, just to finish it. It's like "and then he woke up, and realized it was all a dream" ; except not quite as bad as that makes it sound. Intellectually (sherlock holmes reader style) you could see it coming, but somehow story-arc-wise not so much.
I was totally on board with the story right up to that point though, so definitely good craft.
(edit: was it deliberately a Shaggy Dog Story? If so the fact that there is a trope called "shoot the shaggy dog" is almost too on the nose, so I'm wondering if you had that in mind! https://tvtropes.org/pmwiki/pmwiki.php/Main/ShaggyDogStory https://tvtropes.org/pmwiki/pmwiki.php/Main/ShootTheShaggyDo... )