When teenagers who were reported missing are suspected of a series of mass murders in Chicago, the BAU investigates their whereabouts to find a motive for the crimes. Also, Morgan has conflicting feelings when his girlfriend takes her job at a hospital as seriously as he takes his.

The BAU must track down a killer who sends their victims a warning before poisoning them with arsenic, without ever seeming to come in contact with them.

A terrorist hacks a passenger's tablet and uses it to take control of the auto pilot of a plane in order to crash it.

On October 30, 2014, a frightened eleven year old Joshua Parker is found at a Halloween fair in San Diego. He went missing on Halloween day the previous year. His case mimics that of Tommy Wilcox, who went missing on Halloween 2012 in Los Angeles, only to be found on Venice Beach October 30, 2013, alive but he who eventually died of malnutrition a few hours later. Joshua, however, is expected to live. Both boys had atrophied muscles, and had splinters and puncture wounds, although Joshua seems to have been fed somewhat properly. Both boys were also considered troubled, Joshua who was never listed officially as missing since he was a chronic runaway. The problem for the BAU is that Tommy's captor, Rodney Tanner, who confessed to the crime, is currently incarcerated, meaning that he either had a partner, there is a copycat loose, or that his confession is a lie. They have to figure out this issue before another troubled early or pre-teen Caucasian boy is abducted in the next day. Reid comes to the conclusion that the boys were housed in a homemade wooden box, which accounts for all their physical issues. Discovering a case similar from the past of boys so confined, especially as it relates to Halloween, may provide clues as to the identity of the unsub.

The BAU is stumped to find the common denominator among male victims in Montana, making it difficult to profile the UnSub. Meanwhile JJ deals with her feelings about a family crisis.