Ana is a fifteen-year-old freshman in Dolphin House at Harding-Pencroft Academy. Following the tragic accident that killed her parents two years prior, she relies heavily on her older brother and her tight-knit group of roommates. She unexpectedly finds herself thrust into a leadership position when her school falls under attack, forcing her to confront the heavily guarded purpose behind the academy's existence.

Dev is Ana's eighteen-year-old brother and a senior at Harding-Pencroft Academy. As the captain of Shark House, he focuses heavily on tactical, militaristic training and is known for constantly being in motion. He is a popular student who acts as Ana's sole remaining family member after the death of their parents.

Nelinha is a freshman in Cephalopod House attending Harding-Pencroft on a scholarship. She is highly intelligent and skilled in applied mechanics, engineering, and technology. She hides insecurities about her background behind a confident, stylish exterior and fiercely defends her close friends.

Ester is an autistic freshman in Orca House who specializes in biology and healing. She processes overwhelming information using an elaborate system of index cards and relies on her dog to manage environmental stress. She possesses a deep knowledge of the school's historical secrets and feels an intense responsibility toward its legacy.

Gemini, widely known as Gem, is the freshman prefect of Shark House. He fully embraces his house's militaristic, tactical focus and arms himself heavily when danger strikes. Initially seen as abrasive by students in other houses, he demonstrates fierce loyalty when assigned to protect his classmates.

Dr. Hewett teaches Theoretical Marine Science at Harding-Pencroft Academy. Students generally dislike his class, viewing his subject matter as wildly impractical. During a severe emergency, he drops his academic exterior to issue military commands and protect the students, revealing he knows far more about the world's dangers than he previously let on.

Socrates is a young, intelligent male bottlenose dolphin who frequents the waters around Harding-Pencroft. He actively engages with Dolphin House students and proves willing to put himself in physical danger to protect his human companions.

Luca is a former Harding-Pencroft student and past captain of Cephalopod House. He lives in isolation at a highly classified facility, spending his time maintaining advanced machinery and cooking vegan meals. He provides crucial context about the older generation of students.

Ophelia is a former Orca House captain who lives off the grid. She helps run a classified installation and quickly steps in to organize the surviving students, offering them shelter, guidance, and hard truths about their situation.

Caleb is a student at the Land Institute, the bitter rival school of Harding-Pencroft. He actively participates in the assault on the freshman class, demonstrating his school's aggressive and ruthless methodology.

Franklin is the freshman prefect of Orca House. True to his house's focus on healing and biology, he concerns himself with the physical wellbeing of the other students during their escape.

Tia is the freshman prefect of Cephalopod House. She represents the engineering students in leadership discussions and steps up to handle logistical defense challenges when the group splits up.

Top is a highly trained emotional support dog belonging to Ester. He travels with the students and provides essential grounding services.

Jupiter is an intelligent orangutan residing at a remote facility. He communicates with the humans using sign language and possesses a strong, specific passion for culinary television programs.

Romeo is an enormous Pacific octopus encountered by the students in the open ocean. Initially presenting a terrifying physical threat, his behavior proves complex and requires specialized communication to manage.

Linzi is a student in Orca House. She takes her house duties seriously, acting as a neutral ethical observer during tense interactions with captured enemies.

Originally known as Prince Dakkar, Captain Nemo is a historical figure whose technological genius created a lasting legacy. His inventions and bitterness toward colonial powers set the foundation for the conflict between Harding-Pencroft Academy and the Land Institute.