Joyce Magruder (Catherine Curtin) is the hidden main villainess from "Light My Fire," episode 1.09 of Bull (airdate December 13, 2016). She is a real estate maven operating in the town of Kavanaugh, New Hampshire, the childhood home of Dr. Jason Bull.
In the town, Peter Walsh is accused of setting fire to a diner he worked at, which killed his boss and the diner's owner, Charles Keller. Joyce is first encountered by Bull and Benny Colón early in the episode, with Joyce displaying a chipper demeanor at first. The accusations towards Peter were mainly due to the fact that the Walshes were considered outcast, and Joyce added flame to the proverbial (and literal) fire with her gossip; using her status to influence the jury into believing that Peter was guilty. She antagonized Bull and Marissa Morgan when she voiced her anger over the pair convincing the town of Peter's innocence, while also boasting that she had influence over the jury.
This led to Bull spreading gossip of his own about Joyce: that she was developing a massive condo in the small town. The townspeople bought the story and after Benny's closing argument, Peter was acquitted. Fire chief Walt Simonds revealed that one of his firemen, Sam Keane, burned down not only the diner, but other homes, including a cabin that belonged to Bull's father. Even after the true arsonist was revealed, Bull suspected that Keane doing so under someone's order, and that someone ended up being revealed as none other than Joyce.
As revealed in the episode's climax, Joyce was not only a gossip, she was greedy and ambitious, and as Bull and Marissa revealed, Joyce paid Keane to set the fires. Joyce's plan was to make money in real estate by capitalizing on the arsons, with the villainess stating that all she was guilty of was capitalizing on unfortunate events. The pair also revealed that Keane flipped on Joyce, and that she would be charged as an accessory to murder. In response, the evil Joyce stated to Bull that she always hated him, right before she was arrested.