Supernatural (2005)

S6E16 ...And Then There Were None

In "...And Then There Were None," Eve, the Mother of All, introduces a terrifying new creature: a black worm-slug capable of invading the brain and inciting murder. Sam and Dean team up with Bobby and Rufus to hunt down this deadly entity, tracing it to a cannery. There, they encounter Gwen and Samuel, who are also on the hunt for the monster. The group soon realizes that they are all in the dark about the true identity of the creature lurking among them, raising the stakes as paranoia and danger escalate.