Robie is a teenage girl who usually lives on the remote Midway Island with her parents. She travels to Honolulu to visit her aunt and enjoy the luxuries of civilization, such as Wi-Fi and fast food. After a frightening encounter on the street leaves her feeling vulnerable, she impulsively boards a cargo flight home to escape her newfound independence. When the flight crashes into the Pacific Ocean, she must rely on an emergency raft, a bag of Skittles, and her own untested resourcefulness to stay alive.

Max is the young copilot of the cargo flight bound for Midway Island. Following a catastrophic engine failure, his quick thinking and physical capability are instrumental in getting the life raft deployed. On the open water, he shares stories of his past in eastern Oregon, including his time as a high school wrestler. These conversations provide Robie with a vital link to humanity while they drift across the ocean.

AJ is Robie's aunt, a busy professional who lives in a secure Honolulu apartment building. When she is suddenly called away to California for work, she sets up a loose supervision plan for her niece. She completely trusts Robie to stay safe in the apartment alone, completely unaware of the terrifying events that will follow her departure.

Robie's parents live on the isolated Midway Island at the western end of the Hawaiian archipelago. While they do not appear directly in the early chapters, they represent the safety, protection, and structured life Robie initially wishes to escape. When danger strikes, they become the primary focus of Robie's desperate longing for home.

Larry is the experienced pilot of the cargo plane that resupplies Midway Island. He is familiar with Robie from her previous flights and easily agrees to let her hitch a ride home on short notice, bypassing standard ticketing procedures out of friendliness.

Bobbi is a friend of AJ living in Honolulu. AJ tasks her with checking in on Robie daily during the business trip to California. A sudden injury prevents Bobbi from fulfilling this duty, inadvertently giving Robie complete and unsupervised freedom.

Brandy is a girl from Max's hometown in eastern Oregon. They began dating around homecoming in high school and quickly became an inseparable couple. Max shares fond memories of their relationship to pass the time on the raft and keep morale up.

Starbuck is a baby Hawaiian monk seal that Robie encounters on the uninhabited Lisianski island. Named after the coffee chain Robie deeply misses from civilization, the young seal provides Robie with a sense of companionship and optimism in an otherwise desolate environment.