Last week on "Chicago Fire," Herrmann testified in court against Freddie, describing the attack in vivid detail. But later, he decided to forgive Freddie for stabbing him when Freddie's father, who is a convicted murderer, called Herrmann and asked to talk to him face to face.

Freddie's father took responsibility for his son's actions and blamed himself for the way he treated Freddie. In the end, Herrmann asked the judge to go easy on him as he still wanted to help him in spite of what happened and because he also wanted both of them to heal.

This week in the episode titled "The Sky is Falling," Firehouse 51 finds itself in a deadly situation when a shooter targets a school in the neighborhood.

According to the synopsis for the episode, the firehouse goes on high alert after mysterious threats begin to emerge throughout the city. The situation turns dire when news of a mass shooting takes members of the squad and truck right to the middle of a devastating scene.

In the promo for the episode, Severide (Taylor Kinney) tells the chief that there is a guy on the roof. A man standing at the bottom of a staircase fires his weapon, and children are seen running out of a school as a shooter aims at them. The team is inside the school as several shots ring out, and some of the firefighters try to comfort the frightened children who are still inside the school.

It appears that something big will happen in the episode as the promo teases that this is "the defining moment for 'Chicago Fire.'"

Elsewhere in the episode, Lt. Casey (Jesse Spencer) works to investigate the missing money from the fundraiser for the victims of the recent tornado. Meanwhile, new firefighter Jimmy (Steven R. McQueen) takes one for the team as he agrees to represent the firehouse in the first annual "Battle of the Badges" boxing match against the 21st district police department.

"Chicago Fire" airs Tuesdays at 10 p.m. on NBC.