Thirty years after the Federation thought they had been defeated forever, the Borg returned stronger than ever and ravaged the Milky Way galaxy. Faced with such overwhelming force, the great empires of the Alpha Quadrant fell. Only a few million people remain free of the Collective, spirited away through an unstable wormhole that deposited them within a small satellite galaxy orbiting our own. But their one-way passage took them through time as well as space, leaving this last remaining vestige of humanity a century into the future in a completely unknown region of the universe with no way back, and a mysterious signal being transmitted from somewhere in the assimilated Milky Way.
The USS Euryalus is a small argo-class science vessel. It and a dozen other Starfleet and civillian ships are all that remains of the Federation, and have gathered at a point in space where a wormhole to the Sagittarius Dwarf Elliptical Galaxy, a small satellite galaxy 10,000 light-years from the Milky Way and the only possible refuge from the unstoppable Borg invasion. But the wormhole linking the two galaxies is ancient and unstable, and no probe sent from the Starfleet ships has transmitted data back from the other side. With time running out, the Euryalus is selected to venture through the wormhole. After a rough passage, the small vessel emerges into a completely unknown part of the universe, into a galaxy only a tenth the size of the one they come from. The wormhole however was even more unstable than they first thought, burrowing erratically through time as well as space.
The Euryalus may have been the first ship to enter the wormhole, but it is one of the last to have emerged in the Sagittarius Dwarf. They discover that they have been brought over a century into the future, and that most of the surviving Starfleet ships have already been in this place for nearly a decade.