“Rules of Engagement” is episode eighteen of season four of Star Trek: Deep Space Nine.
This episode opens with Worf having a nightmare before waking up in one of Odo’s holding cells. The Klingon Empire is trying to extradite Worf for his actions in a recent battle. On one of the Cardassian worlds there had been an outbreak of a disease. The world is close to the Klingon border, and the Cardassians had insufficient warships to provide escort for the relief ships. Fearing Klingon attack, they asked the Federation’s help in escorting them. The Federation agreed, and one convoy was escorted by the Defiant commanded by Worf.
The convoy came under attack by two Klingon warships. In the middle of the battle, a civilian warship suddenly decloaked; Worf believed it was one of the warships, and opened fire, killing everyone on board. The Klingons are using the trial as leverage against the Federation.
This is essentially a court case episode. Various people are called to give testimony, which is odd at times, as they are speaking in court but apparently at the point when they are testifying. Sisko is trying very hard to find something to use against the Klingons in the case, but things aren’t going well.