Season 1, Episode 1:
Dean: Dad hasn't been home in a few days.
Twenty-two years ago, Mary Winchester was killed in the family home by an unknown supernatural creature, in front of her husband John and her sons, Dean and Sam. In the present day, Sam is a law student at Standford University with a girlfriend and a promising career -- until Dean arrives, asking for help in tracking down their father. John has been on one of his frequent "hunting" trips, where he tracks down and kills supernatural creatures: John and the boys have been doing this since their mother's death, but Sam left the hunting life after a falling out with his father. John hasn't returned from his latest trip, and Dean is worried.
Sam agrees to help Dean look for their father. They manage to come across the last creature he was hunting, a Woman in White, and destroy her. They also find John's journal, full of all his information on various creatures as well as the record of his hunt for the creature that killed Mary, but they can't find John. Sam returns to Stanford, but when he returns to his dorm, he finds his girlfriend suspended on the ceiling, bleeding and consumed by fire: the exact same way his mother died. Now that it's personal, Sam agrees to partner up with Dean and return to hunting, hoping that along the way they can find their father and finally destroy the creature that killed their mother.
- Beware of Hitch-Hiking Ghosts
- Blue Eyes: Mary and Jessica
- Creepy Child: Constance's children
- Danger Takes a Backseat
- Disappeared Dad: The central plotline for the first season is kicked off when Dean comes to get Sam for Stanford because John's gone missing.
- Double Standard Rape (Female on Male): Averted when Constance tries to forcefully take Sam.
- Driven to Suicide: Constance Welch
- Foreshadowing / Harsher in Hindsight: Sam and Jess' seemingly-innocuous little exchange:
Sam: What would I do without you?
- Great Big Book of Everything: John's journal. Dean steals it back from the police when he is temporarily taken into custody.
- Hair of Gold: Mary and Jessica
- Horror Doesn't Settle for Simple Tuesday: A double-whammy: it's Halloween (October 31st) and later on the anniversary of their mother's death (November 2nd).
- Insistent Terminology
Sam: You know, Sammy is a chubby twelve-year-old. It's Sam, okay?
- Killed Off for Real: Mary Winchester and Jessica Moore
- Kill It with Fire
- The Lost Lenore: Sam is haunted by Jessica's death for a noticeably long time.
- Missing Mom
- Naughty Nurse Outfit: Jessica's Halloween costume.
- Offing the Offspring: Constance drowned her own children before jumping off a bridge and committing suicide. They get their revenge at the end of the episode when their spirits drag hers to Hell.
- Our Ghosts Are Different
- Rain of Blood
- Sacrificial Lamb: Mary and Jess
- Sentient Vehicle: The ghost possesses the Impala and uses it to chase down the Winchesters and force them off the bridge.
- Stuffed in The Fridge / Disposable Woman
- Temporary Love Interest: Jess for Sam
- White Sheep: The source of Sam's two-year-long estrangement from his family is his decision to go to college.
- Woman in White: The ladies in this episode start the fine Supernatural tradition of white dresses showing that the character wearing said dress is either evil, dead, or both.
- Your Cheating Heart: The Monster of the Week's M.O. is to target men who are cheating on their significant other. Subverted when she targets Sam anyway with the funky ghost logic that she'll make him unfaithful.