9-1-1.

Based on Season Four...

Ashleigh's sister Danielle arrives in Los Angeles, but will Ashleigh speak to her? In the aftermath of the dam break, massive mudslides wreaked havoc. Buck and Chimney must rescue a group of pregnant women trapped in a submerged house. And Ashleigh spends the day with Athena...

Buck has a hard time keeping secrets, especially after what Danielle tells him, but when Ashleigh and Danielle's parents arrive in town, how will Ashleigh react?

Buck tells Danielle she needs to tell Ashleigh the truth, so Danielle reveals a painful family secret that causes Ashleigh to confront her childhood and answer why she is the daredevil she is today. Meanwhile, Hen's mother unexpectedly arrives and announces she is moving to LA.

Athena and the 118 race to save lives after a drunk driver causes a deadly pile-up going the wrong way on the freeway and are shocked to discover who two of the injured is. Athena uncovers a secret Bobby has been hiding that puts their marriage on the rocks, and Maddie struggles with adjusting to motherhood.

In the aftermath of the shooting, Athena and the 118 are on high alert when a sniper targets members of the LAFD.