Supernatural - Season 1, Episode 20, Dead Man's Blood
Dead Man's Blood
After Daniel Elkins, a vampire hunter and John's mentor, is murdered, Sam and Dean are surprised when John himself shows up to solve the case. John discovers the vampires have taken an antique gun, which has the power to kill all supernatural beings. The Winchester family sets out to retrieve the gun from the vampires so they can use it to kill the demon that took Sam and Dean's mother.