Alicia is a twenty-year-old mathematical prodigy and doctoral candidate specializing in topos theory. After graduating from the University of Chicago at age sixteen, she struggles with severe depression, synesthesia, and vivid visual and auditory hallucinations. Her deep disillusionment with mathematics and academic life leaves her yearning for a more traditional existence, though she remains highly analytical and intensely philosophical.

Dr. Cohen is a psychologist tasked with treating Alicia during her stay at the psychiatric hospital. He possesses a genuine desire to understand her profound intellect and complex worldview. He maintains a patient, probing demeanor while attempting to ground Alicia's metaphysical ideations, often finding himself outpaced by her encyclopedic knowledge of mathematics and philosophy.

Bobby is Alicia's older brother, a physicist who transitioned into a career as a race car driver and salvage diver in Europe. Using his inheritance to fund his racing, he lives an adventurous lifestyle before a severe accident leaves him comatose. He serves as Alicia's primary emotional anchor to the physical world.

The Kid is a vivid, persistent hallucination who appears to Alicia as a bald dwarf with flipper-like appendages wearing a kimono. He functions as a cryptic companion, communicating through nonsensical dialogue, wordplay, and references to nonexistent books. Despite his abrasive demeanor, he acts as a psychological buffer, attempting to distract Alicia from her darker thoughts.

Miss Vivian is another of Alicia's vividly realized hallucinations. She manifests as an older, deeply eccentric woman who weeps uncontrollably out of profound empathy for the suffering of infants. Her constant sorrow amplifies Alicia's own sensitivity to the pain inherent in the world.

Alicia's father is a deceased physicist who worked under Robert Oppenheimer at Los Alamos during the development of the atomic bomb. He viewed his work on the bomb without remorse, believing it catalyzed necessary global modernization. His involvement in the creation of a mass casualty weapon heavily shapes his daughter's cynical worldview.

Alicia's mother worked as a calutron girl at the Oak Ridge facility, checking dials on uranium without understanding the true nature of the project. She suffered from severe mental health struggles and hospitalizations before passing away when Alicia was twelve.

Leonard is a psychiatric patient and friend of Alicia who resides in a hospital after burning down his family's farm. He desires simple happiness, a goal his counselors frequently dismiss as entirely unrealistic.