The 118 faces an earth-shattering emergency that shakes the city of Los Angeles to its core. Still finding her footing as a detective, Athena leans on instinct to crack a mysterious new case, while May finds her own confidence in a new job.

As lava takes over Los Angeles, the 118 works to evacuate scared and trapped citizens. Meanwhile, Athena runs into a familiar face as she searches for a way out of a collapsed tunnel, and Maddie is forced to make an impossible decision.

In the wake of the volcanic eruption, Maddie and the 118 race to divert a river of lava before it consumes a packed hospital. Athena, still trapped underground, faces a massive obstacle that cuts her off from any chance of calling for help.

Buck and Eddie's friendship is at odds following their argument over Theo. Meanwhile, the 118 races to the scene of an accident that has been complicated by a good Samaritan.