On Teen Wolf Season 6 Episode 13, which was directed by Tyler Posey, Brett's sister, Lori, goes to Scott after she finds the broken lacrosse stick with Brett's blood all over it.
The pack decides to divide and conquer. Scott, Malia, and Liam join Lorie out in the woods to try to track Brett. Meanwhile, Corey and Mason go to Lydia to see if sh can trigger a premonition to discover where Brett is.
They aren't the only ones looking for Brett. Gerard is out with Monroe, training her on how to properly hunt a werewolf, and how to take down an entire pack. Thankfully, Scott and Malia slowly figure out that they aren't dealing with one amateur hunter.
Melissa tries to take a sample of the body with no face, but something about it freaks her out so badly that she runs out of the room and calls Argent for help. When Argent gets there, the body also sends him into a fit of terror. After finally getting a sample, Melissa discovers that the body has no cellular structure, no DNA, which is impossible.
Lydia's premonition reveals the number 68. It's not until she runs into Nolan, aka the kid who just stabbed a pencil through Corey's hand in the library, that Lydia discovers what it means. Nolan is number 68, and he just passed a test by exposing Corey's supernatural abilities to the library.
People are afraid of the supernaturals in this town, and they are starting to turn on them.
After Scott gets wounded in the sewer tunnel thanks to a trap, he and Malia figure out that Gerard's one of the hunters. Unfortunately, at that point Liam and Lori had already left to go find Brett. They still think they are dealing with amateur hunters, but Gerard proves that he is not one to be underestimated.
Lori and Brett go above ground and are promptly run over with a car, killing Brett. Liam jumps up after them in full werewolf mode. Gerard arranged it so that there would be an audience, and sure enough, there are a bunch of scared onlookers watching a very bloody Liam, with his fangs and claws out, angrily pant and roar.