Stardate 50814.2: After finishing up a long survey mission in the Gamma Quadrant, the tired crew of the Defiant heads back towards the wormhole. On their way, Jadzia Dax spots a planet with an unusual barrier around it. With the science officer confident that taking a look a the planet would not cause any problems, the Defiant passes through the planet's atmosphere. The barrier causes damage to the ship and they have to land to make repairs. As they look around for a place to set down, they are hailed by the inhabitants of the planet, who are the great-grandchildren of the Defiant's crew. The barrier created a temporal distortion, sending them back to the past by two centuries.
When the Cardassian occupation of Bajor ended in 2369, the mining space station Terok Nor was left abandoned, its systems ripped out. By invitation of the Bajoran provisional government, Starfleet stepped in to oversee the rebuilding and day-to-day operations of the newly christened Deep Space Nine.
The years of Starfleet's nonintervention into Cardassian matters, however, had taken its toll on relations with the Bajorans. Consequently, Starfleet's position was a tenuous one; many Bajorans, suspicious and hostile as a result of decades of Cardassian oppression and brutality, did not greet the Federation's presence with open arms. The Federation's assistance is put to the test as DS9 becomes a center of travel and commerce that stretches into the Gamma Quadrant.