David Lassiter is a shapeshifter who comes from one of Chicago’s five ruling monster families. David left his family to try and live a normal life as a human, but the murder of his brother Sal Lassiter pulls him back in.
David has shifted to look like a professor at North Chicago University to steal answers to a math final. Upon leaving the building he gets a call from his sister Margo, who tells him that his brother Sal has been killed and that he needs to come home. When David arrives, he asks Margo what happened to Sal, and she tells him that he was killed by Julian Duval and they plan to go to war with the werewolves. David next goes to see his ailing father, who is lying unconscious in bed. David attempts to dissuade his sister from jumping into war so quickly, and that they need to be smart and find out what really happened. But Margo dismisses him, telling he has no part in the matter.
David decides to shift to look like Freddie Costa and visit the only witness to Sal's death -- Ennis Ross -- to question him about what he saw that night. When David 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 Ennis' father to come home, not knowing of Freddie Costa's relationship with the Ross family or that Nate Ross is deceased, David agrees. 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 David to reveal himself as a shapeshifter to Ennis and proceeds to tell him how Chicago is divided up by five monster families, and that Ennis is in way over his head before making his escape.
David later goes to the Duval Estate where he has a talk with Violet Duval where he tries to get her to get her brother to have a sit down with Margo, which leads to them talking about their relationship when the hooded figure appears and attacks David, and kidnaps Violet. Sam, Dean and Ennis rush over to see what happened, and escape the ground with David before the families security can get to them. 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 to search for Violet. David is captured by the hooded figure who is a human named Irv Sokolowski, who then proceeds to cut David with his silver claw, this causes Violet to transform and break free and attack Irv. Before she can kill him, David frees himself and talks Violet down, who reverts back. Sam, Dean and Ennis arrive in the aftermath, where Ennis kills Irv in revenge for killing his girlfriend.
The next day David and Violet are walking together on Duval Estate, when David questions why Sal's last words were "David, I'm sorry. I didn't have a choice." Violet tells him she doesn't know, and the two share a kiss before they go their separate ways. Later at the Lassiter residence, David is sitting with his father who awakens to tell him that his sister wants to go to war, and that he needs to stop her. David lays out Irv's silver claws on table telling Margo the Duval's are clean of any part in Sal's death, and telling her his intention of coming back to the family, for which Margo welcomes him home with a hug.