When three unusually attractive young adults rent the summer cottage next door, Barney's boring vacation at the beach seemingly takes a turn for the better. However, after the neighbors unwittingly reveal their extraterrestrial identities, the board game they have taught him becomes a real-life battle, and Barney must outsmart the aliens to save Earth from destruction. The fantastical tale contains some of Sleator's most inventive characters.

Barney is all set to spend two weeks doing nothing at his parents summer house.  But then he meets the neighbors, and things start to get interesting.  Zena, Manny, and Joe are not your average folks on vacation.  In fact, Barney suspects they're not from Earth at all.  Not only are they physically perfect in every way, but they don't seem to have jobs or permanent addresses, and they are addicted to a strange role-playing game called Interstellar Pig.  As Barney finds himself sucked into their bizarre obsession, he begins to wonder if Interstellar Pig is just a game.