Charlie and the team grapple with the concept of 'randomness' while trying to find a killer targeting drivers on the freeway.
- A man and his two kids are driving in a van on the highway. Someone shoots him and the son has to stop the van.
Cut to Charlie lecturing. "People make decisions irrationally. They see patterns in randomness."
Don visits the hospital and interviews the man's children; they may have seen a white truck. There have been multiple road shootings in the last two months.
The FBI discusses them but can find no M.O. Charlie suggests that all the murders may be actually random and that the patterns may be in people's heads.
Based on the boys' interviews, Meghan thinks a white truck might have been stalking the family. Don interviews the wife with no result, but Meghan keeps searching for patterns. She thinks the lack of patterns in the crimes is in itself a pattern. Charlie admits it's possible but doesn't think it likely.
A connection is found; two victims used the same car wash. They go to the car wash looking for Calvin Oates, who runs but is caught. A customer at the car wash had accused him of stealing money, but he is in anger management therapy and was in class while one of the murders happened. Then another murder is reported.
Charlie and Larry discuss overly random events, and Charlie realizes that the lack of patterns actually represents a shuffling of methods rather than actual randomness. Meghan finds more incidents that confirm the pattern and that the attacks are increasing in frequency. Meghan thinks it is the classic serial killer pattern.
The FBI realizes that many of the victims have had prior involvement in serious accidents. Re-interviewing the original victim, Don learns that he had given a witness report of an accident to police. Charlie thinks he can help with an analysis of traffic patterns; since the killer is planning so carefully, escape routes that the killer might have chosen might be evident.
After mapping traffic, the mathematicians notice that traffic tended to mysteriously open up around the scenes, as an escape route. Another attack occurs, this time on a woman who had turned down a request for a traffic light at an intersection where a serious accident later took place. A victim of that accident is known to be in therapy for control issues. The FBI arrest him, but he turns out to have a bad hand, a bad leg, and concentration issues as a result of the accident, and denies knowing the final victim. They dismiss him as a suspect.
Charlie shows them his escape route analysis and FBI goes to interview people on the route. One man describes a white pickup truck that blew by after a shooting, and also had the traffic light change for him.
The FBI thinks the murderer has a device used by emergency vehicles to force lights to change. Using traffic cameras they get some pictures of the truck, and manage to identify a decal on it for a head trauma support group. They find a suspect based on the group; he's attacking people who hurt others in the group. They find and arrest him as he plans another attack. He had been in an unsolved hit-and-run accident and was taking out his anger through the attacks.
Later, Don wonders if the work is worth it. Charlie suggests a plan to solve the hit-and-run, and Don is right back into it.