Someone who practices a dark Afro-Caribbean religion has been killing people in the barrios of Miami. After he kills them, he stuffs shells in their eyes and in mouths. The BAU travels to Miami to put a stop to the killings before he can strike again. They visit the home of the last victim to search for evidence and clues where they meet Jimmy Mercado, a local at the soup kitchen who knew the last victim, Julio Ruiz, the man who runs the soup kitchen and Elian, Julio's teenaged assistant. Both Julio and Elian practice Santeria, but neither of them wants to talk to the police.
Garcia sends the team to the University of Miami to meet with Professor Hollis Walker. They talk to him in hopes of learning more about Santeria and other regional religions. Professor Walker informs them these killings may be related to another dark religion, Palo Mayombe, which has bizarre rituals that include severed human heads. Professor Walker informs the BAU team that he is nearly finished writing a book on the topic – the only book to be written on the subject. The meeting is cut short with the news that Jimmy Mercado has been found dead. It appears the killer is seeking out the people who had spoken with the FBI.
The team returns to the soup kitchen to find a Santeria service in progress. They break up the service and bring Julio back to the station to question him further. While questioning him, the team discovers that Julio had been jailed for 15 years for being part of a gang that had mutilated the body parts of its enemies. Reid realizes that, while the evidence points toward him, Julio is not the man they seek because he expressed genuine remorse for what he had done in the past. Reid believes that Elian seems a bit suspicious. The BAU finds drugs and other remnants from the previous victims in Elian's room. By the time the team had arrived at his home, Elian had already left. With the help of Julio, they begin their search for Elian.
It is discovered that Elian had been framed. Some of the crimes fit the profile of the Palo Mayombe rituals, but some crimes did not. The team is unable to find any fingerprints, but they do find a bloody footprint on the ground that matched a shoe found in Elian's room. Prentiss and Morgan are the first to figure it out. Professor Walker had committed the crimes and had framed Elian to create more press for his upcoming book.
Julio had been kidnapped during their search for Elian. They don't find any trace of him while they were on the hunt for Professor Walker. While searching, Reid walks out of the main building toward a chapel and finds the killer and Julio, who has been tied up. Reid is able to outsmart the killer. The team arrives in time to arrest Walker and rescue Julio and Elian.
For several days, Reid had been suffering from hallucinations and bad headaches, and goes to the hospital for an MRI. Although everything appears to be all right, his doctor believes he may be suffering from stress.