A massive tsunami hits the Santa Monica Pier, placing Buck and Christopher's lives in danger .

A series of freeway car accidents leads to a catastrophic overpass collapse that endangers the lives of civilians and members of the 118.

Athena, Maddie, Bobby and the 118 races to save lives after a massive tsunami hits the Santa Monica Pier and Buck fears the worst when Christopher goes missing.

The 118 races to the rescue when the 9-1-1 Call Center goes up in flames. Then, Bobby risks his life to save a trapped May, and Claudette, Buck and Eddie work together to help an injured electrician, and Chimney and his brother team up as firefighters for the first time.

The 118 race to the rescue when a structure collapse at a "happiness convention" traps people under rubble. While on FaceTime with her mom, Athena's father suffers a stroke and crashes through the wall of his house. Hen stretches herself too thin with test prep and her new responsibilities at the 118, while Maddie tries to help new recruit get his bearings at the call center.

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

The 118 responds to a fire at a local animal shelter and races to evacuate all the animals. Meanwhile, Maddie takes a 9-1-1 call that sets her on a quest for answers.

Maddie fears for herself and her co-workers when the call center is taken hostage.

A series of ransomware threats leads to an overabundance of emergencies for the 118, including a medevac helicopter crash at a hospital and an air-traffic control tower system failure. Meanwhile Athena must revisit her traumatic attack when the case of the realtor serial rapist goes to trial, Eddie suffers a health scare and Maddie's postpartum depression worsens.

Despite the case being closed, Bobby is determined to prove his AA sponsor was murdered and bring his killer to justice; Meanwhile Buck struggles with his post-traumatic stress.

When a murder weapon from a case close to Athena in the early '90s resurfaces, flashbacks to 1989 show how Athena joined the LAPD and became the police officer she is today.

In the aftermath of the shooting, Athena and the 118 are on high alert when a sniper is targeting members of the LAFD. Meanwhile, Maddie makes a life decision. Season finale

A dry thunderstorm rolls over LA, bringing in a series of lightning strike emergencies for the 118 and leaves a first responder's life hanging in the balance. Athena and May go undercover at the rehab facility to help Bobby with his investigation into his sponsor's mysterious death. Maddie dreads her parents visit to her and Chimney's new and unfinished house, while Chimney get a surprise of his own from a visiting Albert.

Athena and the 118 race to save lives after a drunk driver causes a deadly pile-up on the freeway. Meanwhile, Maddie goes into labor and Hen and Karen are devastated as they prepare their foster daughter, Nia, to be reunited with her birth mother.

Athena's only chance of surviving and saving everyone on the flight is to attempt to land the plane before it crashes and call on the 118 for help.

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

When a blimp suffers mechanical failure and its engine catches fire, Athena and the 118 must rescue victims both inside and outside a packed sports stadium. Bobby and Athena drop off May on her first day of college and discuss honeymoon plans, while Maddie and Chimney go to couple's therapy.

Athena is tasked with safely delivering a prisoner to testify on a high-profile case. Meanwhile, a light plane is hit by a swarm of bees and sent careening into a passenger plane.

The 118 responds to a call at a megachurch, where Bobby runs into his estranged mother. Buck is looking to expand his social circle now that Eddie has left.

In part one of a two-part episode, the 118 is called to a research lab that has been set on fire and becomes a biohazard.

Emergencies include a skating mishap at an ice show, an accident involving a self-driving car and a fulfillment warehouse robot going rogue. Meanwhile, Eddie's after-hours fight club gets out-of-control and Hen struggles in her relationship with Karen.

The 118 rush to save lives in the aftermath of a massive train derailment.

The 118 race to save the lives of workers trapped in a five-alarm factory fire. Meanwhile, Maddie reveals a painful family secret that causes Buck to confront his childhood and answer why he is the daredevil he is today.

The members of the 118 make calls to save a bridezilla at a disastrous wedding and to a mother trapped on her balcony. Meanwhile, Hen plays medical detective when her mother, Toni, falls ill. Also, Eddie and Christopher receive a visit from Carla, Athena uncovers a secret Bobby has been hiding that puts their marriage on the rocks and Maddie struggles with adjusting to motherhood.

After a mysterious death, Hen and Chimney put their lives in danger when they suspect that someone is playing God to make themselves look like a hero. Meanwhile, Eddie visits Texas, where he attempts to reconcile with his father.