As the unexpected arctic cold front and ice storm continues to cause havoc in Austin, Tommy, T.K. and Gillian race to rescue a young boy who has fallen in a frozen pond. Judd and Mateo work furiously to help a trapped Paul, and Owen takes drastic measures to save a man who has been stabbed and left for dead.

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.

The 126 crew responds to a military tank on the loose in downtown Austin and a human pile-up at the roller derby. Meanwhile, new paramedic captain, Tommy Vega, joins the team and Owen is reunited with his ex-wife and T.K.'s mother, Gwyneth, and receives an update on his cancer.

Judd is shocked at the latest victim of an emergency call, Grace and Carlos must save a woman literally trapped in a domestic abuse situation and the 126 arrive at a horrific highway crash that threatens the lives of a father and daughter. Meanwhile, Owen and Gwyneth face a difficult decision in their relationship and Mateo regrets his new tattoo.

Owen makes a decision about his future. Tommy receives devastating news. T.K. and Carlos worry about adopting Jonah. Mateo gets his immigration status threatened after an altercation. A doomsday prepper gets trapped in a bomb shelter and The 126 and all of Austin brace for an asteroid crash.

Owen Strand, the lone survivor of his Manhattan firehouse on 9/11, takes his progressive philosophies of life and firefighting down to Austin, Texas, where he helps the firefighters of Firehouse 126 start anew.

The crew race to a brawl at a male strip club, a fire at a bull semen factory and a protest where male toxicity is taken to a new level; Grace tries to reconnect with Judd; Owen faces the consequences of his chemo.

Owen, Tommy & the 126 race to the rescue when a medieval-themed restaurant suffers a case of carbon monoxide poisoning. Meanwhile the crew is worried that Paul still has not mentally recovered from his surgery and his friendship with Marjan is over. Mateo is offered a promotion by his old fire captain, but quickly realizes he is not the man he once knew.

The members of the 126 race to find, and then save, a mystery victim in a car crash. Meanwhile, Owen faces a crisis in his relationship with Catherine. Tommy goes on a first date and Carlos is surprised when he meets T.K.'s AA sponsor.

Owen and the 126 deal with the aftermath of the asteroid crash in Austin while an even greater threat looms.

Judd calls out Owen's preferential treatment of T.K.. Marjan feels ostracized at her new mosque after another rescue video goes viral. Owen helps Michelle uncover new information about her sister's disappearance.

The 126 is on the scene when a disastrous wedding comes crumbling down, as Grace helps a dominatrix and her slave involved in a shocking situation. Meanwhile, Owen and Gwyneth struggle to label their new relationship and a man from Marjan's past re-enters back in her life.

The 126 race into action when a horse barrels into a brewery with an unconscious rider on its back and then to a bus full of tourists all experiencing seizures. Judd introduces Owen to Wyatt's mother Marlene. Carlos and T.K. start couples counseling, when Carlos investigation into his father's murder becomes all-consuming.

Owen travels to Los Angeles to confront his estranged father and some painful childhood memories. Wyatt acts out and prompting Judd to take him to his family ranch where an emergency brings them closer to together.

Judd literally walks into the line of fire when an armory catches on fire, sending bullets flying everywhere. Owen questions Judd's pledge of sobriety. Marjan introduces boyfriend Joe to her parents, Waleed and Nasreen, but their dinner doesn't go as smoothly as she hoped.

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.

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.

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.

The 126 race into action when an armored truck and its guards are attacked by a group of masked men. Carlos, in his new job as a Texas Ranger, is assigned to investigate the case. Owen attends group therapy with Tommy to deal with his brother Robert's death; Both Marjan and Paul each apply for the open lieutenant position, replacing Judd, who finds himself lost without his old job. Wyatt begins work at the call center and a major train derailment signals tragedy.

The 126 race to save a man crushed under a vending machine. While struggling to handle his aggressive foster horse, Owen finally faces the truth of his brother's death. As Mateo and Nancy scramble to delete a nude photo of her accidentally sent to the 126, Tommy is concerned that Nancy may be facing a possible health scare.

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.

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 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.

TK gets a huge surprise on his 30th birthday when his stepdad Enzo arrives in Austin along with TK's young half-brother Jonah; Owen's resentment of Enzo turns physical; Tommy is determined to push through her latest crisis; Wyatt attempts to talk-down a suicidal caller and the 126 must perform a dangerous surgery in the field after a man is impaled in a tree.