After the disastrous explosion of their moon Praxis that has led to an ecological disaster on their homeworld, the Klingons offer peace talks to the Federation. The Enterprise welcomes a Klingon delegation aboard, but after their return the Klingon ship is fired upon and Chancellor Gorkon is shot by assassins. McCoy attempts to help the dying chancellor in vain. He and Kirk are arrested and convicted by the Klingons. After the Enterprise has freed them from the penal colony on Rura Penthe, they head for the Khitomer peace conference. Here, with the help of the USS Excelsior and Capt. Sulu, they defeat the Bird-of-Prey of the treacherous General Chang and save the life of the Federation President, who was the next on the assassination list. It turns out that it was a joined conspiracy of Klingon and Starfleet officers together with the Romulan ambassador, who all wanted the cold war to continue.