Four interwoven stories that occur on Halloween: an everyday high school principal has a secret life as a serial killer; a college virgin might have just met the one guy for her; a group of teenagers pull a mean prank, and a bitter old recluse receives an uninvited guest.
Ba'al travels back in time and prevents the Stargate program from being started. SG-1 must somehow restore history.
SG-1 searches for an ancient weapon which could help them defeat the Ori, and discover it may be in the Ori's own home galaxy. As the Ori prepare to send ships through to the Milky Way to attack Earth, SG-1 travels to the Ori galaxy aboard the Odyssey. The International Oversight committee have their own plans and SG-1 finds themselves in a distant galaxy fighting two powerful enemies.
