After twenty years of incarceration, Miles O'Brien is released by his Argrathi overseers into the hands of the Federation. However, nothing has changed much. The Argrathi means of punishment is to implant their prisoners with memories of being incarcerated for a length of time. In truth, the prisoner is only held for a while, but the prisoner remembers everything about their long time behind bars. With O'Brien released, his healing can begin... but only if he wants it to.
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.