Lt. Severide is set to step his foot into a dangerous scenario in "Chicago Fire" season 4 episode 20. Also, Casey is set to get a stunning news from his mail.

"Chicago Fire" season 4 episode 20 is entitled "The Last One For Mom." According to Spoilers Guide, Lt. Severide is left with no choice but to watch over Detective Holloway's young son at the firehouse while she attends a court trial for being involved in an undercover operation.

As per the publication, the situation is going to have an unforeseen flow of events, which leads him to face the consequences. Episode 20 is also set to see the firehouse deal with a blaze at an art gallery, with a victim trapped inside. Due to this scenario, Cruz has to decide quickly to resolve the conflict.

Meanwhile, Casey is also set to get a suspicious item from his mail with regard to the Board of Ethics. According to the publication, the said item heightens his curiosity and suspicion about things.

Episode 20 is also set to see Brett learn that Otis is not being responsible in responding to his own issues, leading him to confront the latter. Brett also discovers that Otis is not doing something, but to rally the teams to push a trip to Las Vegas for a firefighting conference, which is held yearly.

In "Chicago Fire" season 4 episode 19, entitled "I Will Be Walking," Casey tried to use his political power to resolve a conflict while Otis learned something that had him fearing for the most adverse thing to take place. According to Spoilers Guide, this discovery led the latter to become very concerned on his actions.

"Chicago Fire" season 4 episode 20, "The Last One For Mom," is set to air on Apr. 26.