Ennis Ross is a resident of Chicago, his father was a police officer who died in the line of duty years ago. He has one sibling, a sister, and claims that his mother is "out of the picture."
Ennis has taken his girlfriend Tamara to the upscale restaurant Il Secundo, where he plans to propose to her. When speaking with the matre d' Maurice about doing something special with his proposal he is interrupted by Sal Lassiter, who Maurice turns his attention to. When Ennis begins to protest, he glances the reflection of Sal's bodyguard Marv in the mirror, which reveals a monsterous appearance. Shaken by what he saw, Ennis quickly leaves the restaurant with Tamara and takes her to a ferry stop where he intends to finally propose to her. But before he is able to, a severely injured Sal Lassiter arrives and collapses in front of them. As Ennis and Tamara attempt to help him, a hodded figure appears and slams Tamara against a rolling steel door, cracking her head open and killing her.
The next day Ennis is being questioned by Detective Freddie Costa about what he saw that night, refusing to change his story. Sam and Dean Winchester soon arrive posing as FBI agents to question Ennis. After some time Ennis is released and heads to his home, once there he begins looking through a trunk that belonged to his father, where he finds a revolver and, hidden in box, silver bullets with something carved in them. Later Ennis breaks into the back room of Il Secundo, where he sees broken glass, claw marks, blood all over the place. When Maurice enters the room with a mop and bucket, Ennis hides behind the bar, however Maurice is able to sniff him out. When Ennis pulls a gun on him, Maurice reveals himself to be a vampire, as Maurice is about to attack Ennis, Dean Winchester cuts his head off with a machete. When Ennis refuses to leave, until he is told what just happened, Sam gives him "the talk" and reveals to Ennis that monsters exist, and that they are hunters. When Ennis wishes to join them on the hunt to find what killed Tamara, he is dissuaded by Sam who tells him he's better off not getting into it.
Ennis heads back to his home where he begins looking into Sal Lassiter's background, when Freddie Costa suddenly shows up to question him some more about what he saw the night Tamara died. When Freddie begins asking him questions Ennis had already answer at the precinct, Ennis becomes suspicious and asks Freddie if he wants to hang around and wait for his Dad to come home, which Freddie agrees to. Realizing some thing is up, and remembering what Sam told him about monsters being able to be seen through mirrors and cameras, Ennis pretends to get a text and turns on his phone's camera which reveals Freddie to have a retinal flare. Ennis leads Freddie to another room where he quickly distracts him and pulls a gun on him, telling him there are silver bullets in the gun. This leads "Freddie" to reveal himself as David Lassiter -- a shapeshifter -- a proceeds to tell him Chicago is divided up by five monster families before making his escape.
After his encounter with David, Ennis beings researching Julian Duval and stakes out the Duval estate at the same time Sam and Dean are. When Irv Sokolowski attacks David and Violet Duval; Sam, Dean and Ennis rush over to see what happened, and David joins them in there escape from the Duval estate. After the Winchesters have been caught up with David being a shifter and the five monster families, the four team up and track Violet down by tracing her cell phone signal. They arrive at an abandon warehouse, and split up and search for Violet. Sam, Dean and Ennis arrive in the aftermath of Violet and David freeing themselves from Irv. When Irv looks up and sees Ennis, he tells him he is sorry about killing his girl, but that he should understand because he was killing monsters. However, Ennis tells Irv he's the only monster he sees, shoots and kills him.
After the whole ordeal, Sam tells Ennis that he will contact other hunters to deal with the monster situation, and again tries to dissuade him from getting involved in hunting before they leave. Ennis chooses not to heed Sam's warning, loads his fathers revolver with silver bullets and goes back to Irv's hideout. While looking at Irv's clippings, Ennis gets a phone call, the man other end tells him not to start hunting, because the monsters will kill him and hangs up. This leaves Ennis in a state of shock as he believes the man that just called him was his long deceased father.