Lt. Severide is set to respond on a perilous scenario while Casey is set to get a stunning item in his mail in "Chicago Fire" season 4 episode 20.

"Chicago Fire" season 4 episode 20 is entitled "The Last One For Mom." According to Spoilers Guide, Lt. Severide will be entrusted by Detective Hollaway to watch over the latter's young son at the firehouse while she reports to a court trial for being part of an undercover mission.

As per the publication, the situation is set to take an unforeseen flow of events, which leaves Severide to act on the event's impact on him and the people around him. It is added that the firehouse will attend to a blaze at an art gallery and the team learns that a victim is trapped inside. This leads Cruz to think and decide in the middle of things.

Meanwhile, Casey is set to get a doubtful package in the mail, which leads him to suspect on the Board of Ethics. Details on the source of the item and its impact on Casey are yet to be revealed. Also, Brett learns that Otis is not dealing with his problems, so he confronts the latter; however, the former discovers that Otis is willful and more eager to rally the troops and set up a travel to Las Vegas in line with the yearly firefighting event.

In "Chicago Fire" season 4 episode 19, entitled "I Will Be Walking," Casey was seen trying his best to resolve an issue concerning a high school student, who became a victim of a gang retribution incident. As per Spoilers Guide, the episode also saw Severide agree to help Detective Holloway watch over her son at the firehouse. Also, Brett and Jimmie are tasked to help a woman who seems to like Jimmy.

"Chicago Fire" season 4 episode 20, "The Last One For Mom," airs on Apr. 26.