Invasion of the Micronauts
by Ian Tullis and Mike Selinker
The pdf appears to be blank, but a tiny off-white dot is in the lower half of the page. Blowing it up to 6400% gets this image:
These words can combine with the six kinds of quarks, which have unique lengths: passing STRANGE, bikini BOTTOM, lucky CHARM, hunt DOWN, big TOP, do UP. If these quark names are placed in the same grid, the shaded letters spell TROOP.