S4, E10: The Firehouse is shocked to discover that one of their own becomes the surprising victim of a stabbing, and an attempted suicide raises some questions - a three-part story arc crosses over into "Chicago Med" and concludes the following night on "Chicago P.D.” Members of Firehouse 51 band together and anxiously await word at Chicago Med when one of their own falls victim to a life-threatening stabbing. Cruz (Joe Minoso) urgently works with members of Chicago P.D. to track down Freddie's (Ralph Rodriguez) whereabouts when he goes missing. Dr. Choi (guest star Brian Tee) and Dr. Halstead (guest star Nick Gehlfuss) tend to an attempted suicide victim whose condition raises some eyebrows. Meanwhile, Mouch (Christian Stolte) surprises Trudy, (guest star Amy Morton) and Chili's (Dora Madison) odd behavior has Brett (Kara Killmer) and Jimmy (Steven R. McQueen) worried.