It is Halloween night and all the kids are dressed in scary and funny costumes. Their Trick or Treat bags are getting heavier. Nate's good friend Rosamond needs his help. Her cat, Little Hex, is missing. Little Hex hates Halloween, so maybe he's hiding. Or is he lost? Nate and his trusty dog Sludge take the case and hunt in the night for Little Hex. They pass robots, a dancing artichoke, pirates, and witches. But where will they find Little Hex?