A Federation captain is attacking Cardassian ships, and O'Brien meets his old commander.
The Enterprise is sent to meet with the Cardassians, a species new to the series, to help in the peace process that has ended a long war. A Federation captain named Maxwell, however, has been attacking Cardassian ships, convinced that the peace is a trap. Picard has to stop him before the war starts again.
The episode introduces the Cardassians and Chief O'Brien's backstory as a veteran of that war, and includes the first appearance of Gul Macet. It is a story about the cost of war and of the damage that it does to the people who fight in it. The Cardassians would go on to play a major role in later series, particularly Deep Space Nine.