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.

Captain Strand and the 126 race to the rescue when a woman is trapped in her mobile house that has been hijacked by her ex. Owen has a run in with former nemesis Sgt. O’Brien and is then questioned by the FBI. Tommy asks Grace dating advice. T.K. and Carlos meet with Iris Blake.

As Owen gets pulled deeper into the FBI’s investigation of the motorcycle gang, Sgt. O’Brien makes a confession to him. Meanwhile, Grace and the 126 respond to a call from a man who claims his girlfriend slipped over the side of a cliff and Carlos searches for a missing friend, putting his own life in danger.

As Owen wears an FBI wire for his meeting with O'Brien, The Honor Dogs crash the meet-up and let them know there's an infiltrator in their midst. A frantic TK desperately searches for a missing and held captive Carlos.

Owen helps defend Marjan when a rescue complaint forces her to make a challenging ethical decision. Meanwhile, Grace befriends a young boy who becomes a frequent 9-1-1 caller, but when she discovers he may be in some real danger she must step in.

Capt. Strand reveals to the 126 he has been working with the FBI to help bring down a domestic terrorist group with his Austin motorcycle club/gang The Honor Dogs, then race Owen to respond to a bomb threat at the State Capitol and put a stop to the terrorist deadly plans.

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.

The 126 must rescue a father/son involved in a drivers ed lesson gone haywire, then encounter a self-help guru who has lost his self-control. Meanwhile, Owen turns into a "Dadzilla" in helping plan T.K. and Carlos' wedding, and Marjan is suspicious when she meets a couple on her road trip.

On her way back to Austin, Marjan is in for the fight of her life when she is targeted by a killer.

Tommy goes paramedic crew-to-crew against her former employer, private contractors Paragon Medics, as they deal with emergencies involving a dialysis patient and at a perfume factory. Meanwhile, Owen hits it off with a beautiful woman he meets at a fundraiser.

The 126 race to rescue a woman with an arrow shot into her head; Judd is doubly surprised by news Wyatt shares; Mateo helps a family member in need and comes to regret it.

When she discovers her former fiancé is having a baby with his new wife, The 126 help Marjan enter the dating world through a series of chaperoned dates; Owen and the team are called to the rescue when a pregnant woman takes matters (and her anger) out at a motel where she suspects her husband is cheating on her.

Owen is shocked by a secret Kendra has been keeping from him; Grace confronts her father about his past infidelity.

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

Grace and Carlos work together when they suspect a young woman was a victim of a black market organ trafficking ring; Owen's brother Robert comes to visit and meet T.K., but surprises Owen with news that can affect the Strand family.

When Tommy and Judd disagree on protocol during a rescue at paper mill, a full-on feud develops between the 126 EMS and Fire. Owen awaits news that could change his and T.K.'s lives forever.

Owen is conflicted when his brother Robert asks him for help; Judd and Grace face a family crisis; As T.K. and Carlos prepare for their wedding day tragedy strikes.