As the rest of SG-1 prepares to join Landry (Beau Bridges) and Mitchell (Ben Browder) on a retreat, Teal'c (Christopher Judge), who is assisting the SG-3 team, discovers that the inhabitants of a distant planet are being mutilated by a savage and elusive alien creature. While SG-1 fears the Ori's sinister work is at play, they soon discover the creatures are being created by a parasite not indigenous to the planet. Meanwhile Mitchell and Landry are the object of surveillance while staying at General O'Neill's cabin. As SG-1 receives word that the creatures are appearing on other planets are also, Mitchell discovers some hunters who have been the victim of a similar attack on Earth. Desperate to find the origin of the parasites, the team makes an alarming discovery: not all planets affected by the attacks were visited by the Ori, but they were all recently visited by SG-1. Horrified to discover that they could somehow be at fault, SG-1 must determine how to stop the creatures before they kill again.