Stargate Atlantis (2004)

S2E16 The Long Goodbye

The team stumbles upon two alien pods housing the consciousness of extraterrestrial entities. These beings seize control of Weir and Sheppard, using their bodies to wage an ongoing conflict from their past. As the situation escalates, the team must find a way to reclaim their friends and halt the destructive battle ignited by the aliens' unresolved vendetta. Tensions rise as the line between friend and foe blurs, forcing the team to confront the true stakes of their mission.