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 veteran with a live grenade embedded in his leg. Meanwhile, Buck gets a surprise visit from his sister, Maddie. Also, Athena questions her relationship with Bobby. Then, at the fire station, handsome new hire Eddie jeopardizes Buck's chances of being chosen for a fireman calendar.

The first responders continue to deal with the fallout of a massive earthquake and its deadly aftershocks. Athena tries to keep the peace as Bobby and team continue to rescue victims from a collapsing high-rise hotel, both under the rubble and high above the ground. Maddie's first day on the job involves helping a pregnant couple deliver their baby safely.