William Sleator's Interstellar Pig (1984) is a book I'd encountered as a young adult. I'd forgotten it (blocked it?) entirely until Bex mentioned it a few weeks ago. And then, when she realized I hadn't read it for decades, she thrust it into my hands and stood over me until I finished. "Encountered" and "blocked it" are deliberately pejorative words. This supposed children's book is exactly the sort of thing that breaks fragile young minds. Not because it is bad - more the reverse: Sleator's hallucinogenic science fiction is way too well-written.
Barney is a lonely, slightly-geeky 16 year old with parents that "just don't understand" (in fairness to Mr. Sleator's characterization, he does a great job creating the distant/loyal Charlie Brown style parental unit). His miserable summer is enlivened when three very peculiar strangers move next door and entice him into playing their favorite board game.
The game is, of course, the titular "Interstellar Pig". Each player assumes the role of an alien - the representative of their entire species. The aliens quest around the universe in search of the "Piggy", an artifact of unknown origin or value. When the timer goes off, the alien holding the Piggy is spared. All the other species - and their homeworlds - are extinguished.
As you can probably predict, the game and Barney's reality become cataclysmically intermingled. Barney is pursued by alien lifeforms while desperately trying to save Earth. What should be a fairly goofy YA scenario is turned into very real horror by Mr. Sleaton's extremely evocative prose. And, of course, the enticing descriptions of the actual game - guaranteed to trigger the imagination of any geekishly-inclined reader.