The FBI's Behavior Analysis Unit (BAU), a team of seven elite senior agents, continues to travel around the country, providing excellent criminal psychological profiling and criminal behavior analysis for real cases. Aaron Hotchner, a rigorous and capable supervisor, chose to stay in the BAU in order to continue to track down serial killers. His wife divorced him and took away their six-year-old son. David Rossi, a senior agent, voluntarily returned to join the BAU with a knot in his heart after more than ten years of retirement. He gradually got used to the new model of the BAU and integrated into the team. Derek Morgan, who is confident and humorous, is an expert in crime reconstruction. He is never soft when fighting criminals, but he is a regulator of the active atmosphere in the group. "Genius" is the most concise interpretation of Dr. Spencer Reid. He has a super memory and is a living case book. Shy and strong, he has been tested several times and finally gradually walked out of the shadow of drug addiction. Jennifer Jareau (JJ), who is in charge of public relations, also began to learn and master profiling knowledge. She is busy with work and has been keeping a low profile in her "long-distance relationship" with detective William. She is pregnant and is facing new adjustments at work. Emily Prentiss, who has been in the group for a year, has a tough style but is very friendly. As the daughter of an ambassador, she is fluent in Arabic, Spanish and Russian. With her rich experience in handling cases and strong observation skills, she has been fully recognized by everyone. Technical analyst Penelope Garcia is an indispensable active element and technical support for BAU. After a near-death experience, she found love after recovery. At the end of last season, BAU faced a difficult case that happened in New York. Unknown suspects with completely different styles of committing crimes randomly shot pedestrians on the street, and the location of the crime did not conform to the conventional profile... After the SUV carrying a member of BAU exploded, how will the fourth season reveal this suspense? How will the remaining members save their cherished colleagues and continue to track down the murderer behind this deliberate terrorist attack? The new season will continue to touch the nerves of the audience of "Criminal Minds" on September 24.