The interception of the Klingon sleeper ship T'Ong, whose crew were about to wake after seventy-five years still believing the Empire was at war with the Federation.
In The Next Generation episode The Emissary, the Enterprise-D picks up a special envoy who arrives in a cramped probe: K'Ehleyr, half Klingon and half human, and a former lover of Worf. She brings word that the battle cruiser T'Ong, launched some seventy-five years earlier with its crew in suspended sleep, is nearing Federation colonies in the Boradis system.
Its captain, K'Temoc, and his crew know nothing of the peace and will attack the first outposts they see. A Klingon ship is too far away to help. K'Ehleyr sees no choice but to destroy the T'Ong, which Picard is reluctant to accept.
Worf offers another way. When the T'Ong decloaks and opens fire, he appears on the viewscreen in Klingon uniform as captain of the Enterprise, with K'Ehleyr beside him, and orders K'Temoc to stand down. Faced with Klingons in command, K'Temoc obeys.