SGC is baffled as several 'fake' SG-1 and a few other SG-teams keep arriving through the Stargate, which has to be blocked. The various Carters and Dr. Lee realize this must be the result of an a time-space singularity, presumably triggered by a black hole, causing a one-way passage between parallel universes which prove different in many details -like uniforms- and some more significant ways, like a live Dr. Janet Fraiser urgently needing help to cure a Prior plague and Carter's beloved Tok'ra, Martouf. Key proves to be the black-uniformed SG-1, whose Carter inspires a joint mission using the Prometheus, which proves an elaborate trap as they hijack it to save their own universe, resulting in a battle of matching wits.
—KGF Vissers