Masks (Star Trek The Next Generation, No 7)

But shortly after transporting, Picard and his party lose contact with the ship, and Commander Riker leads a search party down to the planet to find them.

Both men, are unaware that their searches, indeed, the ship's entire mission are part of the plan of a madman, a madman who is setting the stage for a trap that will ensnare both U.S.S. Enterprise landing parties, and leave him to seize control of the awesome Wisdom Mask as well as the planet Lorca itself.