SG-1 finds a planet inhabited by Native American Indians, protected by spirits who are actually advanced alien shapeshifters.

SG-1 discovers an elderly man known for developing technology to fight the Goa'uld. Daniel is tricked into switching bodies with the man, Ma'chello, who believes he is "owed" for all the good he has done.

When Daniel goes insane, SG-1 must deal with the legacy of Machello's anti-Goa'uld technology.

SG-1 must free an alternate reality Earth from a Goa'uld invasion after duplicates of Samantha Carter and Charles Kawalsky come through the quantum mirror.

SG-1 encounters an entire planet suffering from amnesia. The planet's leader returns to Earth with SG-1 to find a cure, but SG-1 suspects she may not be who she appears to be.

SG-1 receives alien brain implants that manifest themselves as a bizarre man, who tells them that they would not survive the procedure to remove him.

When a member of the SGC tries to kill a Tok'ra, it is revealed that O'Neill and Carter may be victims of an untraceable form of Goa'uld mind control.