The USS Enterprise NCC-1701A arrives at Beta XII-A after a distress call has been received. On arriving, a Klingon Bird of Prey arrives. When the crew visit the planet, the Klingon beam down to and arrest the away party. The Klingons demand control of the Enterprise because their ship is no longer functioning. Capt. James Tiberius Kirk agrees to beam the crew up to the Enterprise but tricks the Klingons and holds them in stasis.
When the Klingons are finally beamed onboard the Enterprise, the Klingons are held in security. Its not long before Klingons start proving difficult. Pavel Chekov announces he wants to kill the Klingon in revenge for his brothers death at the Klingons. Lt. Hikaru Sulu reveals to Kirk that Pavel Chekovs an only child.
When Kirk confronts the Klingons, the Enterprises' phasers are turned into swords and other objects are turning into swords giving the Klingons a way to fight back. An alien entity is causing illusions and causing people to act irrationally including Spock. It transpires that an alien force is causing the problems and the only way to defeat it is not what the alien creature wants. Kirk agrees with the Klingon to pretend to be friendly with one another including laughing.