Dash and his best friend Assaf are navigating their sophomore year at Tides High School, which precariously rests on a cliff above a fault line. Together, they contribute to the school newspaper, under the guidance of their mutual friend Verti. However, everything takes a turn when Verti decides to assign Assaf a solo piece on the grand opening of the new auditorium situated on the top floor. Observing the budding rapport between Assaf and Verti ignites a sense of betrayal in Dash, leading him to pen a scathing article about Assaf that leaves a lasting mark on his permanent record, much to Principal Grimm's dismay.
In a quest for redemption, Dash infiltrates the school archives to uncover his record, but instead, he stumbles upon incriminating evidence that reveals Grimm's forgery of the auditorium inspection report. During this escapade, he encounters Mary, an ambitious junior on a mission to retrieve her confiscated cellphone. Their attempt to alert the student body about the misplaced trust in their school administration lands them in detention, coinciding with the disastrous opening of the auditorium, which causes the school to plummet into the ocean.
In a moment of chaos, Dash bravely rescues Assaf and Verti from the sophomore library. Verti devises a plan for them to navigate through the seawater by utilizing trapped pockets of air to breathe. Though Dash finds himself in a near-drowning situation, he is saved by Lunch Lady Lorraine. Meanwhile, on the junior floor, teachers struggle to maintain order among the surviving students. Lorraine steps in to quell the rising tensions and showcases her unexpected survival skills by rescuing Verti from a group of unruly students dealing drugs. The courageous group, including Lorraine and Mary, decides to make their way to the roof, even though others are hesitant to join.
Upon reaching the senior level, they encounter Brent Daniels who has formed a cult-like group around him. It is at this point they confront Principal Grimm, who admits to his forgery and guides them to scale the auditorium bleachers to reach safety, ultimately sacrificing himself to ensure their escape. The group makes it to the roof just as rescue helicopters descend. Lorraine manages to save several other students, while a few utilize a makeshift raft to reach safety. In the aftermath, Dash and Assaf pledge to document their harrowing experience in a book.
Fast forward several weeks, the surviving students are partaking in a celebration for the release of Dash and Assaf's book titled Our Entire High School Sinking into the Sea. Unfortunately, the reviews are less than flattering, critically addressing Dash's overly complex writing style. As the party winds down, Lorraine reminds Dash that she has an entire new class of students to look after, before she exits the scene.
