The Firehouse 51 crew arrives for another shift. Herrmann, Otis and Dawson are concerned about the fate of Molly's bar; Casey is still trying to recover from the loss of Hallie, and Dawson and Mills still aren't speaking. Before they have time to settle in, the crew is called to a structure fire at the local prison. After a word with the warden, the crew heads into the prison.
Boden radios Herrmann inside to tell him that his wife has just gone into labor. Eventually, the team locates the fire in a crowded jail cell. It's a chaotic scene. The room is filled with smoke and dangerous inmates. As soon as the fire is safely extinguished, the prison loses power, and the firefighters find themselves locked in a dark room with dangerous inmates.
Outside, Boden scrambles to get the power back on, but the prison is locked down until the power grid resets itself. Unwilling to wait any longer, Boden orders Severide and the Squad Team to breech the prison. While Severide struggles to break into the prison block, a guard discovers that the cells in the main prison block have been opened, allowing the inmates to roam freely. The scene is becoming more dangerous by the second.
While Severide struggles to break in to the prison, Boden receives word that Herrmann's wife is undergoing an emergency C-section, but he chooses to withhold the information until the prison situation is extinguished. Meanwhile, inside the cellblock, Casey and Herrmann discover that a guard has been murdered and hidden in an empty cell. The inmates have stolen the guard's keys, giving them access to the entire prison.
In the midst of the chaos, Dawson and Mills find a moment for a much needed heart-to-heart. Otis and Mouch frantically try to get the power back on while Casey, Herrmann and the prison guard keep an army of angry prisoners at bay. One of the prisoners holds a shiv to Herrmann's throat. From outside the prison, Boden is powerless to help his men.
Casey cautiously herds the rioting prisoners to the chapel. Casey tries to negotiate the hostage crisis with Herrmann, but the prisoners are reluctant to compromise unless Casey turns the surviving prison guard over. Meanwhile, Severide breeches the prison doors to save Dawson and Mills. It's a small victory, but they're still far from safe.
Severide finds the prison engineer and puts him on the radio to talk Mouch through an electrical reset. Shay reports that Herrmann's wife gave birth to a baby boy. Herrmann manages to break free from the prisoner, and a full on riot almost breaks out. Luckily, the firefighters manage to lock themselves in an office. Mouch gets the power back on just as Severide opens a vent to flood the room with smoke, incapacitating the prisoners.
After receiving word that the baby might be in trouble, Herrmann rushes to the hospital. Luckily, Herrmann's wife and baby are fine by the time he arrives. Boden tells Mills that the higher-ups have decided not to promote him to Squad. The Chief encourages Mills to keep at it, but Mills is fed up with the politics of the Firehouse. He heads to the police department to fill out an application
Dawson goes to Casey's house to reveal her true feelings. She finds him living in squalor, a broken man since Hallie's death. Dawson will have to put him back together again. Otis learns that a giant sports bar is being built right next to Molly's. Severide learns that Renee has returned to town to inform him that she's pregnant with his baby.