A representative of an alien race that went through drastic evolution to survive its own climate change, Klaatu comes to Earth to assess whether humanity can prevent the environmental damage they have inflicted on their own planet. When barred from speaking to the United Nations, he decides humankind shall be exterminated so the planet can survive.
Libby Parsons, wrongly convicted for her husband Nick's murder, thinks he is still alive and wants to settle the score and find their son. As she has been tried for the crime, she cannot be re-prosecuted if she finds and kills Nick.
Ba'al travels back in time and prevents the Stargate program from being started. SG-1 must somehow restore history.
