The Last One for Mom

S4 E20: Detective Holloway (guest star Jenny Mollen) continues to entrust Lt. Severide (Taylor Kinney) to watch over her young son at the firehouse while she testifies in court as part of an undercover operation. When the situation takes an unexpected turn, Severide is left to deal with the aftermath. The firehouse responds to a blaze at an art gallery that has a victim trapped inside and prompts Cruz (Joe Minoso) to make a rash decision amid the chaos. Casey (Jesse Spencer) receives a suspicious package in the mail that casts suspicion on him from the Board of Ethics. Meanwhile, Brett (Kara Killmer) discovers Otis (Yuri Sardarov) isn't taking care of his own important issues and confronts him, but finds he is stubborn and more interested in rallying the troops to organize a trip to Las Vegas for the annual firefighting conference.