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.

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.

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.

As the unexpected arctic cold front and ice storm continues to cause havoc in Austin, Owen works to rescue the lives of the stranded migrants; T.K.'s life hangs in the balance and Grace prepares for the birth of her baby.

Grace is caught in the ice storm as she goes into labor, and Judd, Owen and Tommy race to find her.

When T.K.'s mother, Gwyn, has an emergency, Owen and T.K. travel to New York. But the flight is anything but smooth when the plane experiences a mechanical failure. Meanwhile T.K. reflects back when Gwyn helped get him into rehab years ago.

Captain Strand and the 126 come together when one of their own is trapped after a building explosion. Meanwhile, Owen reflects on his 9/11 experience, T.K. and Carlos come to a decision and Tommy and Julius decide on their future.

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.