Daughter of a Nigerian mother and a British father, eight-year-old Jessamy Harrison is unlike the other girls at her school in Bromley, England. Spending hours alone reading and drawing, Jessamy is seemingly content in her own company, gifted, difficult, even peculiar, given to screaming tantrums and strange, febrile fevers.
The family visits a bevy of aunts, uncles and cousins in Nigeria, where Jess is surrounded by the warmth and inclusion of her mother's people. On this visit, the solitary Jessamy meets a new friend in an abandoned building - Titiola, whom she names TillyTilly. Jess is delighted with her new playmate, luxuriating in the newfound intimacies secrets and shared experiences.
Most confusing is Titiola's reappearance after the family returns home. TillyTilly even knows all of Jess's secrets: the girls at school who ridicule her difference and lack of social skills, anyone who disturbs or makes the precocious Jess angry. Eventually Jessamy realizes that no one can see her new friend; she is invisible.
At this point the novel shifts from fiction to fable. Is this girl a panacea for her emotional confusion, a figment of Jessamy's imagination, or is there a darker source in the roots of African folklore, where spirits have the power to enter the physical realm? The disturbing incidents increase, and Jess realizes she can't control TillyTilly's appearance or her actions. Fear presides, those closest to Jessamy affected by the sinister presence of this sister-friend who does or doesn't really exist.
Jessamy's parents take her to a therapist, Doctor McKenzie. It is through the girl's response to the therapist that the real image of this tormented child takes shape. It is TillyTilly who tells the shocking secret of Jessamy's birth: she was born a twin, but her sister did not survive.
TillyTilly yearns to take the lost sister's place, but her desire is twisted around her own identity as the missing half of another twin. TillyTilly wields the power, controlling Jess, whose fright grows in proportion to escalating events. As a twin, Jessamy is a child of three worlds: "this one, the spirit world and the Bush, which is a sort of wilderness of the mind," according to Jessamy's mother.
In a desperate struggle for dominance, Jess returns to Nigeria with her family to confront her demons and the fear that rules her life. Here the battle for Jessamy's soul is engaged, a fight waged between two realities, the physical and the spiritual, the living and the dead.
The Icarus Girl is imbued with the language of otherness, a fairy tale in which anything is possible, ancestral rituals in Nigeria, lost twins and imaginary friends part of the fragile warp and weft of Jessamy's existence. The novel was written before author Oyeyemi's nineteenth birthday, capturing both the innocence and deviousness of an unhappy child who cannot find a comfortable place to inhabit, where conflicting emotions are allowed to coexist; instead, folklore mixes with reality, the half-life of the spirits begging recognition.