The Enterprise encounters a sequence of planets that have undergone mass destruction. Worf correctly surmises that the massive damage they see is the scars of war. When they come up on another planet that is similarly scarred and ice-bound, they make contact with a human that is astonished to see humans in command with a star ship. He only has time to challenge Picard and ask him who his overseers are before he is cut down. The Enterprise has come upon a planet where humans are slaves to the Tseetsk, a species of large, intelligent birdlike creatures and the humans have just revolted. The man that was killed was an overseer, a human boss over the slave gangs.
When he realizes who they are, Koban, the leader of the human slaves tries to enlist Picard's help in his battle with the Tseetsk. Although they have lost the ability to maintain it, the Tseetsk are in possession of a technology vastly superior to the Federation's. A tachyon based messenger missile was so powerful that it's mere passage proximate to the Enterprise knocked out several primary systems.
When Picard refuses to immediately take sides, Koban has Troi and him kidnapped and taken to a remote outpost. Their captors then battle with a species indigenous to the planet and learn that all of the planetary damage the Enterprise has encountered was due to a war between the Tseetsk thousands of years before. When two giant Tseetsk ships answer the messenger missile, Riker is forced to try to negotiate with them. Fortunately, in the nick of time, the Enterprise crew is able to locate Picard and Troi, beam them back to the ship with the leader of the indigenous Tseetsk and they manage to reach a peaceful accord.
I found very little tension in this episode, while Picard and Troi are in danger while they are being held captive, it is the slave humans that are nearly all killed. The ending was much too brief, there was not enough buildup to create the suitable tension and everyone was very eager to reach a solution. There was no significant posturing on the part of the slave humans, indigenous Tseetsk or the Tseetsk that arrived in the ships. Everyone put aside their thousands of years of hatred and differences in a matter of minutes, which is very unlikely.