Season synopsis
Contains spoilers for this season and earlier seasons.
Season four keeps SG-1 moving between alien crises and the uneasy work of building allies. A Replicator survives Thor’s ship’s destruction and infests a Russian submarine, where O’Neill and Teal’c fight the machines. Carter accompanies Thor to help defend the Asgard from their own Replicator crisis. The team later works with the Tok’ra, but trust remains fragile: Shan’auc believes she has persuaded her symbiote to reject the Goa’uld, but its apparent conversion ends in betrayal, while the spy Tanith compromises Tok’ra plans. Other missions expose the cost of competing needs, from the Gadmeer ship’s sulfur-based terraforming threatening the Enkarans’ new settlement until SG-1 secures a way to save both peoples, to an experimental Death Glider carrying O’Neill and Teal’c into space.
Trouble also reaches Stargate Command. A coercive Pentagon scheme forces General Hammond out, so O’Neill turns to Harry Maybourne to uncover the leverage used against him and bring Hammond back. SG-1’s ties to the Tok’ra become central in the finale, when Tanith escapes after his treachery is exposed and alerts Apophis to the Tok’ra base on Vorash. Carter and Jacob use a black-hole-connected Stargate to make Vorash’s sun go supernova, destroying the approaching Goa’uld fleet. The shock wave throws SG-1’s ship far from Earth, however, and Apophis’s vessel appears nearby, leaving the team stranded in hostile space as the season ends.