An energy being boards the ship during a delicate diplomatic mission.
The Enterprise is ferrying delegates from two rival species, the Anticans and the Selay, to a peace conference, and the ship must keep them apart while tensions flare. Meanwhile, a mysterious energy cloud passes through the ship, and afterward crew members start acting oddly. The entity takes over Captain Picard himself, and his behavior grows increasingly strange.
The story plays as both a diplomatic comedy and a mystery, balancing the quarrelsome delegates against the unsettling threat of an unknown intelligence loose aboard. It shows early how seriously the series took the Captain's burden of command, and it features Worf and Troi in supporting roles. Fans often remember it for the unusual designs of the two alien species.