The USS Enterprise receives an urgent message from Starfleet Command ordering them to a set of co-ordinates without stating a reason. On arrival they are contacted by Admiral Gromek, who informs them that the Enterprise is to rendezvous with a Federation Emissary who will brief them on their mission. She refuses to disclose any details to Picard, only that Starfleet considers the mission a 'top security matter'.
Data reports that the Emissary is being transported in a class 8 probe, which is only "just over" 2 metres long, traveling at Warp 9. Due to there being no starships nearby which could intercept the Enterprise, and that by sending the Emissary to them instead of diverting the Enterprise they will save 6.1 hours of travel time. Picard notes that Starfleet believes time is of the essence.
The ship meets with the probe and beams it aboard. On opening the probe the crew discover the Emissary to be half-Klingon half-human woman named K'Ehleyr. K'Ehleyr is introduced to the rest of the command staff and its immediately apparent that she and Worf know each other and that Worf is not happy to see her. She informs the command staff that 3 days previously Starfleet picked up a signal from a Klingon battlecruiser called the T'Ong which was launched from the Klingon homeworld over seventy-five years ago, when the Klingons and the Federation were still at war. The message states that the ship is about to reach its 'awakening point', which indicates that the crew has been in suspended animation. It is feared that if the crew awaken they will immediately attack the nearest Federation outpost, of which there are several nearby. To prevent this, Starfleet Command has ordered the Enterprise to intercept them and convince them that the Federation and the Klingons are at peace. Riker asks why they have been given this assignment instead of a Klingon ship, and K'Ehleyr reports that a the nearest Klingon ship won't arrive for 3 days. K'Ehleyr believes the plan will fail and Picard will have no choice but to destroy the T'Ong but Picard refuses to consider that option and orders the staff to come up with alternatives.
Worf is ordered to work with K'Ehleyr, an assignment Worf immediately tries to get out of citing personal reasons. Picard asks if there are professional reasons why he can't work with K'Ehleyr. Worf says no and withdraws his request. During their first meeting Worf and K'Ehleyr have a heated argument, only barely managing to concentrate on the job at hand. At Troi's suggestion K'Ehleyr goes to the holodeck where she uses Worf's exercise program to vent her frustrations.
Worf finds her there and joins her in the program. They are stimulated by battle and each other and it is implied that they spend the night together and mate. As he is then required to by tradition, Worf starts the Klingon vow of marriage, by shouting "tlhIngan jIH" (Klingon for "I am a Klingon"), but K'Ehleyr refuses to take the vow and storms out.
At a meeting of the senior staff K'Ehleyr presents two alternatives when they find the ship: the crew is still asleep in which case they keep them that way until a Klingon ship can meet up with them in 3 days; or the crew is awake in which case they will have to destroy them. Picard still resists the idea of destroying the ship despite K'Ehleyr's insistence that the Klingon captain will not negotiate. They are interrupted by Data, who reports that they have detected a vessel, which turns out to be the T'Ong. Data scans the ship and determines that while there are life signs on board he can't tell if they are awake. He speculates from the ship's low power readings that the crew is still asleep but suddenly the T'Ong fires on the Enterprise causing Data to announce that 'he could be in error'.
K'Ehleyr urges Picard to let the Klingons die with honor, in battle. However, Worf has another option. While Picard and Riker conceal themselves, Worf and K'Ehleyr, clad in full traditional Klingon command uniforms, appear as captain and first officer of the Enterprise, informing Captain K'Temoc of the T'Ong that the war is over and ordering them to surrender. K'Temoc initially refuses believing it to be a Federation trick. But when Worf threatens to destroy the T'Ong K'Temoc grudgingly agrees.
Worf turns control of the ship back over to Picard. Commander Riker, obviously hoping to eventually command a starship himself, asks Worf for his impressions. Worf characteristically speaks volumes in just two words: "Comfortable chair."
K'Ehleyr transports to the T'Ong to begin the process of acclimatising the Klingons to life in the 24th century and await the arrival of the Klingon escort which has been sent to meet them. Before departing, she admits to Worf that she was tempted to take the marriage vow with him and implies that their paths will cross again.