The trial of James T. Kirk and Leonard McCoy before a Klingon court in 2293 for the murder of Chancellor Gorkon, which ended in a life sentence on Rura Penthe.
After Gorkon's ship was fired on and he was shot by assassins in Starfleet suits, Kirk and McCoy beamed over to help. McCoy could not save a patient whose anatomy he barely knew, and both men were arrested. The Federation president declined to intervene.
In Star Trek VI: The Undiscovered Country General Chang prosecutes, using Kirk's own log entry about never forgiving the Klingons for his son's death. Their advocate, Colonel Worf, can do little more than have the death penalty commuted in the interest of the coming peace talks.
The pair are sent to the ice mines of Rura Penthe, where the shapeshifter Martia arranges an escape meant to get them killed. Spock tracks them with a patch placed on Kirk's uniform and beams them out, and the true conspirators are then exposed.