The BAU searches for a motive and an UnSub when victims are found in truck stop restrooms along highways throughout the South.
Leonard, Sheldon, and Wolowitz run into problems when they file for a patent for their infinite persistence gyroscope. Also, Penny, Amy and Bernadette give Koothrappali dating advice.
A Christmas visit from his mother has Leonard discovering she's kept a lot of news from him that she shares with Sheldon and worrying if she'll approve of his romance with Penny.
A squabble over the thermostat setting leads to Leonard going over to Penny's and recounting for her the story of how he met and moved in with Sheldon.
Leonard and Wolowitz try to distract Sheldon when he slows the progress of their guidance system. Also, Penny and Amy take Bernadette out for the night, leaving Raj and Stuart to care for baby Halley.
While at school, Erica attempts to fool Beverly into thinking parents weekend has been rescheduled. Adam joins the school production of "Romeo and Juliet."
Soon after the BAU steps in to help local law enforcement isolate a prime suspect for a ritualistic murder, a second person who is related to the first victim is killed under similar circumstances.