Captains Strand and Vega along with the members of the 126 are called into action to a county fair when a "Derecho," a series of fast-moving severe thunderstorms, hit Austin, causing hurricanic and tornadic-force winds, heavy rains, flash floods and a wide path of destruction. Owen's newfound passion for motorcycling puts him on a potentially dangerous path. Tommy has the potential for a romance when she meets an attractive single father. And as T.K. and Carlos prepare for their wedding, a secret from Carlos' past may stand in their way to happiness.

Capt. Strand and the 126 help a husband whose wife "dies" when she is not upside down. Grace takes a call from a pizza delivery driver who is in for the shock of his life. Tommy is worried Trevor's young daughter is a bad seed as she attempts to break them up. Paul is hesitant to go on a date with Asha, who knows him prior to his transition.

Owen enlists Paul's help in proving Kendra's innocence; Tommy deals with church gossipers over her relationship with Pastor Trevor.

The 126 race into action when a major train derailment causes multiple injuries; Meanwhile Tommy makes a bold move in her relationship with Trevor; Wyatt asks Owen to give Judd his job back as Marjan and Paul continue to compete for the open position.

The 126 race to contain a toxic chlorine cloud of death unleashed by the train derailment. Owen names the station's new lieutenant as Judd finds a path forward.

The 126 are called on the scene to a hoarder's rat-infested house, then are trapped in an elevator as a woman goes into labor. Tommy and Trevor host his ex-wife Cassandra for dinner which goes awry.