A heist on an armored truck sparks a Texas Ranger investigation led by Carlos. Owen deals with Robert's death in therapy as Marjan and Paul vie for lieutenant. Wyatt starts at the call center when a train derailment occurs.

The 126 race into action when a major train derailment causes multiple injuries. Tommy makes a bold move in her relationship with Trevor. 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. 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.

A horse barrels into a brewery with an unconscious rider on its back; a bus full of tourists all experience seizures; Judd introduces Owen to Wyatt's mother; Carlos investigation into his father's murder becomes all-consuming.

The 126 race to save a man crushed under a vending machine. Owen finally faces the truth of his brother's death. Mateo and Nancy scramble to delete a nude photo of her accidentally sent to the 126.

TK gets a huge surprise on his 30th birthday when his stepdad arrives in Austin. Tommy is determined to push through her latest crisis. The 126 must perform a dangerous surgery after a man is impaled in a tree.

A gang killing leads Carlos to new information on his father's murder. TK contemplates a major life decision as Owen is determined to get Austin's first responders' health care coverages increased.

Carlos is determined to solve his father's murder. Owen is offered a life-changing opportunity. Judd gives into his demons. Tommy begins her treatment.

Judd literally walks straight into the line of fire when an armory catches on fire, sending bullets flying everywhere; Owen questions Judd's pledge of sobriety; Marjan introduces her boyfriend Joe to her visiting parents.

Owen makes a decision about his future. Tommy receives devastating news. T.K. & Carlos worry about adopting Jonah. Mateo gets his immigration status threatened after an altercation. A doomsday prepper gets trapped in a bomb shelter.

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