S4, E15: Firehouse 51 responds to an odd call from a neighboring firehouse and the unusual circumstances prompt Severide (Taylor Kinney) and Cruz (Joe Minoso) to take the investigation into their own hands to search out the real story. The truck welcomes new firefighter Stella Kidd (guest star Miranda Rae Mayo), but her addition has repercussion inside the firehouse. Meanwhile, Casey (Jesse Spencer) moves forward in his run for alderman, but begins to realize that some voters have their own personal agendas for wanting him elected.