The mastermind is Minuet. Moriarty, in conjunction with rogue Binars, gave her back her sentience, and then she got upset that Riker married Troi instead of her, so now she wants revenge on the Federation. She hired Skullface to do her dirty work for her, and he subcontracted a bounty hunter, Vadic, to carry it out. They claim they're after Picard to throw off the scent. It's really Riker they're after. And that's why he's captured now, along with Troi. Vadic and Skullface are to bring Riker and Troi to Minuet, who'll exact her revenge on both of them.