On one of the hottest days of the year, the first responders feel the pressure as harrowing incidents keep happening around the city, including a road rage accident involving a van full of tourists, an emergency at an auto-repair shop and a grenade. Meanwhile, Buck gets a surprise visit from his sister, and a handsome new hire Eddie jeopardizes Buck's chances of being chosen for a fireman calendar.

The holidays are naughty and nice for the first responders, who must deal with a stampede at a toy store, a mistletoe stunt gone awry and neighbors competing in a Christmas-light showdown. Meanwhile, Bobby contemplates his future with Athena, Chimney and Buck attempt to lift Maddie's spirits and Eddie must decide if he wants to give his son what he really wants for Christmas - a visit with his mom.

Bobby meets Athena's parents for the first time and Maddie attempts to end her marriage for good, causing Doug to insinuate himself even deeper into Chimney's life. Meanwhile, a tanker carrying a tiger shark crashes on the freeway and a gas leak in a plastic surgeon's office happens mid-surgery.

The First Responders rally together to search for a missing Maddie.

Chimney is determined to find a missing Maddie amongst the chaos of St. Patrick's Day.

As Buck's life hangs in the balance, he dreams of a world where he never became a firefighter, for better and worse.

After years of anticipation, Maddie and Chimney's long-awaited wedding day arrives. However, when the groom mysteriously vanishes, the 118 races against time to ensure he doesn't miss the most crucial day of his life.