Episode - 1 [Pilot -aka- Woman in White]

When Sam (Padalecki) and Dean (Ackles) were young, their mother Mary (Samantha Smith) died a violent and unexplainable death, which in turn led their father, John Winchester (Jeffrey Dean Morgan), to teach them skills which they might need in the search for whatever it was that took her life. Years later, while attending Stanford University, Sam is forced back into the paranormal world by his older brother, who has come to tell him that their father has mysteriously disappeared. The two travel to Jericho, California, to find him, but their search is put on hold when they discover that a ghostly Woman in White (Sarah Shahi)—the spirit of a woman who drowned her children and then killed herself—has been taking male victims. They investigate, but Dean is soon arrested for impersonating a federal agent. However, he manages to escape custody, and saves his brother from the vengeful spirit. The Woman in White is finally put to rest after the brothers force her to confront the spirits of her children. Sam later returns home, and discovers his girlfriend Jessica (Adrianne Palicki) pinned to the ceiling. He is then forced to watch as she is killed in the same supernatural manner as his mother. Jessica's death prompts him to return to the life of hunting with Dean.

Episode - 2 [Wendigo]

After having no luck in the investigation of Jessica's death, the brothers follow instructions found in their father's journal and head to Blackwater Ridge, Lost Creek, Colorado. Posing as park rangers, they help a young woman named Haley (Gina Holden) and her younger brother Ben (Alden Ehrenreich) search for their lost older brother Tommy (Graham Wardle), who disappeared while on a camping trip. Sam and Dean soon realize that he was taken by a wendigo that has terrorized the woods since 1936. While searching, Haley

and Dean are kidnapped by the creature, but Sam and Ben are able to track them to a mine. After Dean, Haley, and Tommy are freed, they kill the wendigo with a flare gun.

Episode - 3 [Dead in The Water]

The brothers decide to investigate the drowning of Sophia Carlton, whose body was never found. At the sheriff’s (Daniel Hugh Kelly) office the brothers discover that there have been similar incidents over recent years. They also find out that the local dam is leaking, and will soon drain away. The sheriff’s daughter, Andrea (Amy Acker) and her son, Lucas (Nico McEown) arrive at the office. The brothers learn that Lucas' father was one of the victims, and that the boy witnessed the event and hasn’t spoken since. Lucas draws Dean a picture of a house.

At the Carlton residence, Will drowns in the kitchen sink. Sam and Dean assume that the father, Bill Carlton is somehow involved as the thing in the lake has targeted his children. Lucas provides Dean with a second drawing of a young boy, Peter Sweeney, who vanished 35 years ago with his red bicycle. Dean spots a photo of Peter with Bill Carlton; soon they witness Bill, in a boat, makes his way to the middle of the lake.
The boat explodes.

Dean goes through Andrea’s photo albums, and discovers an old school photo of Andrea’s dad with Peter. Dean assumes that the ghost is targeting their loved ones. Lucas leads them to a spot near the lake where Sam and Dean dig and discover Peter's bicycle. The sheriff holds them at gunpoint, telling them that Bill and he accidentally drowned Peter, and let body sink in the lake. Suddenly Lucas is pulled into the lake by a ghostly hand. The sheriff walks into the lake calling for Peter to take him. Peter drags him under the water, and Dean saves Lucas.

Sam and Dean prepare to leave - Lucas has begun to talk again. As a parting gift, Dean teaches Lucas the phrase ‘Zepplin Rules!

When it came time to name the two lead characters, Kripke decided on "Sal" and "Dean" as an homage to Jack Kerouac's road-trip novel On the Road. However, he felt that "Sal" was inappropriate for the main character, and changed the name to "Sam". It was originally intended for the brothers' last name to be "Harrison" as a nod to actor Harrison Ford, as Kripke wanted Dean to have the "devil-may-care swagger of Han Solo". However, there was a Sam Harrison living in Kansas, so the name had to be changed for legal reasons. Combining his interest in the Winchester Mystery House and his desire to give the series the feel of "a modern-day Western", Kripke settled on the surname of "Winchester". However, this also presented a problem. The first name of Sam and Dean's father was originally "Jack", and there was a Jack Winchester residing in Kansas, so Kripke was forced to change the character's name to "John".

Kripke originally intended for the car to be a '65 Mustang, but his neighbor convinced him to change it to a '67 Impala, since "you can put a body in the trunk" and because "You want a car that, when people stop next to it at the lights, they lock their doors." 
Kripke has commented, "It’s a Rottweiler of a car, and I think it adds authenticity for fans of automobiles because of that, because it’s not a pretty ride. It’s an aggressive, muscular car, and I think that’s what people respond to, and why it fits so well into the tone of our show."

Kripke had the series planned out for three seasons, but later expanded it to five, and hopes to end it there on a high note. Now the network has announced a sixth season, but confirmed that Kripke won't be present in the production.