1. You’re drawn in from the first sentence.
2. You can’t put it down.
3. You find your mind returning to it after you’re done reading.
4. It seems to be about one thing, but turns out to cover larger and subtler territory.
“Companion” is a short story by Sana Krasikov that, for me, fulfilled the admittedly subjective criteria above.
“Companion” was published in The New Yorker in 2005 and is still available on their website. I found it via Longreads, which mostly re-publishes new stuff (as far as I know). But I’m glad that older gems like “Companion” are being circulated for a new audience.