Psi-2000 is a lifeless, frozen world in the final stages of planetary disintegration, an invaluable opportunity for scientific study. But the enter scientific outpost complement is dead, apparently by violence. And soon enough, an odd intoxication of similar nature begins sweeping through Enterprise, threatening all of the crew and even the ship itself, as intoxicated crewmen lose all sense of duty and purpose. Worse, McCoy's investigations reveal no causative agent, limiting his ability to treat those affected.

The Enterprise recovers Harcourt Fenton Mudd from within an asteroid belt. His crew is also his cargo - wives for settlers on Ophiuchus III. These women are very beautiful, and have oddly compulsive effects on the male crewmembers. Having burned out most of her dilithium crystals protecting Mudd's ship, Kirk detours to a Rigel mining colony to secure more. But Mudd's women secure a communicator for him, enabling him to strike his own deal with chief miner Ben Childress and his associates. To obtain the crystals, Kirk must bring down Mudd's women, and must agree to dismiss charges against Mudd. Added to the mix is that the women may not be all they appear to be...