Nicolas is a fragile young boy residing by the sea with his mother. One fateful day, while swimming in the ocean, he believes he spots the lifeless body of another boy, notable for the red starfish adorning his waist. When he rushes home to tell his mother, she dives to the depths and retrieves the starfish, insisting there is no body present. However, that very night, she returns with the boy's body, gathering with a group of other mothers around it in a somber moment.
As the days pass, Nicolas plays with the starfish. However, a confrontation arises when another boy jeers at him for being afraid of it, causing Nicolas to act out in anger, resulting in him severing one of the starfish’s arms. This aggressive outburst leads his mother to take him to a hospital for monitoring. During his time there, a doctor performs a surgical incision just above Nicolas’ stomach, introducing him to a ward filled with other boys who have undergone similar operations.
At night, the nurses engage in watching unsettling videos depicting cesarean procedures. After his release, Nicolas grows increasingly suspicious of his mother and the hospital staff, suspecting they may be hiding significant truths from him. In a moment of rebellion, he and his friend Victor sneak out under the cover of darkness to observe what the mothers are involved in. While Victor scampers back home, Nicolas witnesses a strange scene: the women lying together completely unclothed, writhing in mud and passing a mysterious object among themselves. Upon sneaking a glance at his mother showering off the mud, he notices suckers on her back, deepening his growing fear and confusion.
As events continue to unfold, Nicolas receives an ultrasound and, to his mother’s apparent delight, they hear the heartbeat of a fetus. A drastic turn occurs when Victor undergoes an operation, during which a creature is extracted from his stomach and placed in a jar. Tragically, Victor dies on the operating table, yet the nurses assure Nicolas and the other children that he is recovering. Amidst this chaos, a nurse presents Nicolas with a conch shell, claiming it’s from Victor.
During her visits, Nicolas’ mother attempts to feed him, but he stubbornly refuses and accuses her of not being his true mother when she flips through his sketchbook. In the midst of this turmoil, he forges a bond with a kind-hearted nurse named Stella. She secretly brings him crayons and paper, and they enjoy drawing together. The innocent images Nicolas sketches — including a lifeless boy, starfishes, a bicycle, a car, a building, and even a giraffe — are drawn from memory, hinting at the sinister truth that he might have been taken from another place, along with the other boys who share suspicions about their mothers’ true identities.
As the narrative unfolds, one evening Stella takes Nicolas down to the sea, revealing the suckers on her back and allowing him to touch them before leading him into the water. In a shocking twist, she submerges him until he drowns, only to resuscitate him using CPR. Afterward, Nicolas experiences a traumatic nightmare and sneaks into a different room where he encounters another boy. When he places his hand on the boy's stomach, he feels unsettling movement, and the boy soon begins to vomit. In a harrowing sequence, Nicolas discovers another boy floating in a tank, leading to his capture by a nurse. Following an intense surgery, he regains consciousness, finding himself restrained in a tank, with what appears to be two unborn babies floating alongside him.
In a surreal moment, Nicolas finds himself once again by the sea with Stella. As they swim together, she presses her mouth against his, providing him air to breathe underwater. She ultimately pushes him back to the surface, and they ultimately find themselves in a small rowboat drifting away from the island. After ensuring Nicolas has fresh water to drink, Stella slips back into the sea, seemingly returning to the mysteries of the island. Left alone, Nicolas watches as the day fades and finds himself approaching the harbor of a bustling city, filled with anxiety and uncertainty about what lies ahead.
