The story unfolds with Conor (Lewis MacDougall), a 12-year-old boy trapped in a haunting nightmare where he is clinging to his mother, only to let go as she tips towards an abyss. Waking up, he finds himself in the real world, where his mother, Lizzie (Felicity Jones), is battling cancer, evidenced by her hairless head. Over breakfast, she informs him about her upcoming chemotherapy session and mentions a visit from Conor's grandmother, which Conor dreads. At school, he faces a bully who takes advantage of his vulnerability, further complicating his emotional turmoil.
That night, Conor is jolted awake when a booming voice calls his name. To his surprise, he encounters a towering tree that transforms into a Monster (Liam Neeson). The Monster tells Conor he will share three stories with him, and after that, Conor must tell his own truth, the truth he hides deep within. This exchange marks the beginning of a series of fantastical and educational tales revealing deeper lessons about morality, responsibility, and human complexities.
Conor's grandmother, Gran (Sigourney Weaver), arrives the next morning and immediately begins overseeing Conor's life, much to his displeasure. As tension mounts, Conor struggles with the weight of his feelings—both toward his mother’s condition and his familial relationships. One night, the Monster visitations turn into a cacophony of fantastical tales showcasing moral grey areas. From a prince entangled in his own deceit to an apothecary faced with ethical dilemmas, each story pushes Conor to grapple with his own emotional struggles and grief.
As days pass, Conor finds solace in these tales and begins to act out his frustrations, culminating in an explosive confrontation with his bully at school. Each encounter with the Monster becomes increasingly personal. He faces painful truths about himself, culminating in the revelation that he has called upon the Monster not merely to protect his mother but to heal his own anguish.
In the climax of this journey, Conor is forced back to the edge of his nightmare—the cliff—where he must confront the truth, a painfully human desire for resolution and release. It’s revealed that in order to move forward, he must let go of his mother—not when she dies, but in acceptance of her impending fate. The Monster validates Conor's complexity as a human being, reminding him that it’s natural to wish for an end to suffering.
In the poignant finale, Conor’s emotional journey comes full circle as he and his grandmother find a way to live with their shared pain, cementing their bond through the love for Lizzie. Conor discovers a connection to his mother’s artwork, where he finds a mystical drawing of the Monster, revealing the breadth of their shared experiences and reminding us how stories intertwine our lives in mystical and unexpected ways.
