After a volcanic eruption wreaks havoc in Austin, the members of the 126 race to save lives at a college pool party, a family's mini-golf outing and a woman trapped in her food truck by a horde of scorpions.

As a wildfire spreads across Texas, Evan "Buck" Buckley, Henrietta "Hen" Wilson and Eddie Diaz from the 118 firehouse in Los Angeles arrive in Austin to help Capt. Strand and the 126. As the crews race to save a group of teenagers trapped by the fire at a campground, Owen and Hen fight for their lives in the aftermath of a helicopter crash.

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.

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 and T.K. risk their lives to save two brothers trapped in a homemade minefield. Meanwhile, Grace receives an emergency call from a conjoined twin who's brother is dying, Tommy interviews new candidates to fill the team's open EMT position and Paul's mother and estranged sister pay him an unexpected visit.

The 126 arrive at a funeral where another dead body has crashed the burial, and then to a hospital where an MRI has gone haywire. Owen and Tommy each feel displaced in their homes as Gwyn moves into the Strand household and Charles seemingly becomes the full-time parent in the Vegas'. Meanwhile, T.K. makes waves in his new position.

A bank robbery, an apartment fire and a pregnant woman lost in a parking garage are the seemingly unconnected calls to which the 126 responds. Then, T.K. celebrates his one-year anniversary of sobriety, while Owen and Gwyn may not make it to the end of the week as a couple. Also, Carlos finds himself working on a case with his Texas Ranger father.

Grace and Judd fight for their lives in the aftermath of the horrific car accident, as flashbacks show how a childhood tragedy led Judd to meet Grace and how they ultimately fell in love.

The 126 make calls to a bloody disaster at an ice cream shop and help rescue a boy missing from his own birthday party. Meanwhile, the 126 holds an "intervention" for Owen after he accidentally spills his secrets to new roommate Mateo. Then, T.K. and Carlos take a big step in their relationship, as Grace learns to rely on others in the aftermath of the car accident.

After being forced to take time off work to recover from his surgery, Owen finds himself immersed in the search for a serial arsonist. Meanwhile, T.K. and Carlos take their relationship to the next level and Marjan copes with the aftermath of losing someone on the job.

A recovering Owen becomes the prime suspect in the serial arsonist case. Meanwhile, T.K. and Carlos find themselves in a fiery situation and Tommy gets the surprise of her life.

Owen helps Tommy through a personal emergency.

Owen and the members of the 126 race into action when a massive dust storm engulfs Austin. Season finale