"How to Host a Teen Mystery." Great for slumber parties or co-ed get-togethers, says the squib in Casual Living's mail-order catalogue. The game takes eight players step-by-step through a mystery and solution. Crimes might be arson in the lab or the theft of answers to the Meaningless Aptitude Test. The scene: Hollywood High. If you're game, call the Florida company for a catalogue at (818) 243-6170.