Will is an engineer who designs offshore oil rigs. He is traveling from Hawaii to San Francisco with his 11-year-old daughter. Dealing with the grief of losing his eldest child, Will has become highly cautious and protective in his daily life. His engineering background gives him an analytical mindset, which prompts him to make the critical demand to seal the plane doors after the crash.

Chris owns a marine construction company and works as an industrial diver. She handles crises with a calm, levelheaded demeanor. She often suppresses her emotions to focus entirely on the task at hand. When she learns her family's flight has crashed, she leverages her deep diving expertise to challenge military protocols and design her own rescue operation.

Shannon is the 11-year-old daughter of Will and Chris. She possesses a mature, observant personality similar to her mother's demeanor. She manages her fear by focusing on practical matters, stepping up to comfort a younger unaccompanied passenger. She understands her father's overprotective nature but privately desires more independence.

Kit is the First Officer of the commercial flight. When disaster strikes, she assumes responsibility for the passengers trapped in the sealed cabin. She relies on her training while remaining flexible enough to listen to outside expertise, assigning specific survival tasks to the remaining passengers to maintain order and morale.

Jackie, commonly called Fitz, is the Coast Guard District 14 Commander overseeing the massive rescue mission. He organizes the response involving both military personnel and civilian vessels. He carries the personal grief of losing his own son, which fuels his deep empathy for the victims' families.

Andy is a passenger on the downed flight traveling to Hawaii. He is combative and deeply distrustful of the decisions made by the other survivors, frequently arguing about the best course of action. His confrontational attitude creates friction within the confined air pocket.

Jasmine is a bartender and passenger on Flight 1421. Because she does not know how to swim, she experiences high levels of anxiety regarding the rising water in the cabin. She mixes drinks for the adults from the plane's liquor stash to offer a brief moment of relief.

Ruth is an elderly passenger traveling to Hawaii for a final adventure following a terminal cancer diagnosis. She maintains a sweet and amicable presence in the cabin, offering a calming contrast to the panic surrounding her.

Ira is an elderly passenger on Flight 1421. He exhibits a grumpy exterior but remains fiercely devoted to his wife, Ruth. He insists on taking responsibility for dangerous tasks to protect the younger passengers in the cabin.

Ryan is a young newlywed passenger. The sudden trauma of the crash leaves him largely silent and immobilized. He helps search for supplies once the cabin is sealed, finding small moments to process his immediate grief.

Molly is a flight attendant on Flight 1421. She adheres closely to her training, locating emergency equipment and trying to keep the passengers organized. She works directly with her fellow crew members to secure the cabin as water begins to seep inside.

Kaholo is a flight attendant and a Hawaiian native. He sustains an early injury while helping to secure the cockpit door but remains cooperative and active. As an experienced surfer, his physical fitness proves useful when the group faces difficult underwater tasks.

Bernadette is a nurse and passenger on the flight. She readily applies her medical expertise to treat injuries and monitor the health of those trapped inside. Her knowledge proves vital when the passengers face medical emergencies in the sealed cabin.

Maia is an eight-year-old unaccompanied minor traveling on the flight. After her assigned guardian abandons the plane, the remaining adults and older children take collective responsibility for her comfort and safety.

Noah is a professional civilian diver on Chris's marine construction team. He works closely with his colleagues to execute complex underwater engineering tasks and supports Chris's independent rescue plans.

Peter is a professional civilian diver employed by Chris's company. He follows Chris when she intercepts the military rescue operation, ready to assist her in executing a dangerous plan to retrieve the sunken passengers.

Sayid is a professional civilian diver working for Chris's marine construction company. He utilizes surface-supplied air systems to perform critical underwater welding and technical repairs on the damaged aircraft.

Mikey is a Coast Guard dive officer working under Commander Fitzgerald. He coordinates the underwater aspects of the official military rescue plan, dealing firsthand with the extreme depths and dangers of the ocean shelf.

Steve is a Coast Guard rescuer involved in the surface operations. He assists in monitoring the crash site and relaying vital information between the sunken plane and the command team.

Runt is a 21-year-old Coast Guard diver tasked with a highly dangerous underwater operation. He handles the heavy drilling equipment necessary for the military's initial lift plan.

Patricia is a Navy Fleet Master Chief coordinating the Navy's resources for the rescue operation. She evaluates the technical feasibility of using specialized submarine rescue equipment to save the passengers.

Danny is a Navy officer involved in the technical logistics of the rescue. He initially resists sharing classified blueprints with Chris, preferring to let the military handle the broken equipment.

Caputo is the Navy's lead diver. He advocates for using watertight immersion suits to extract the passengers, accepting the high risks involved with untrained civilians using complex military gear.

Annie is the deceased oldest daughter of Will and Chris. She died six years prior to the events of the novel after an accident at a public pool. Her tragic loss remains the central emotional weight that fractured her parents' marriage.

Ed is the designated guardian for an eight-year-old passenger on the flight. When panic ensues after the crash, he prioritizes his own survival, arguing against sealing the plane and evacuating onto a life raft alone.

Captain Miller is the lead pilot of Flight 1421. He carefully maneuvers the doomed aircraft to fly as far into the crash as possible, maximizing the passengers' chances of survival during the emergency water landing.