Will Freeman, portrayed by Hugh Grant, is a 38-year-old bachelor who takes pride in his laid-back and seemingly "cool" lifestyle. Thanks to the continuous royalties from a hit Christmas song written by his father, Will leads an indulgent life free of work commitments, devoting his days to smoking, binge-watching television shows, and diving deep into the world of pop culture.
The narrative unfolds when Will's friends, Christine (Sharon Small) and John (Nicholas Hutchinson), invite him to take on the role of godfather to their newborn. In a candid moment, he flatly refuses, revealing just how superficial he believes himself to be: “I really am that shallow.” Determined to steer clear of spending time in the presence of the new parents, Will encounters Angie (Isabel Brook), a single mother, with whom he briefly forms a romantic connection. However, seeking further adventures, Will concocts a scheme to attend a group for single parents known as SPAT—Single Parents Alone Together—with the ambition of finding potential romantic interests. To bolster his narrative, he fabricates an imaginary two-year-old son named Ned.
At one of these gatherings, Will crosses paths with Suzie (Victoria Smurfit) and tries to charm her at a picnic, where he meets the intriguing Marcus (Nicholas Hoult). Marcus is a 12-year-old boy, introverted and somewhat unusual, grappling with life under the oversight of his depressed mother, Fiona (Toni Collette). A rather disastrous episode at the picnic sees Marcus inadvertently kill a duck with stale bread while attempting to feed it. To avoid any frightening repercussions, Will steps in to manage the situation, amusingly claiming that the duck was already deceased, all while trying to subdue its body in a comedic yet frantic moment.
Upon returning Marcus home, they are confronted by the devastating sight of Fiona, who has attempted to end her life with an overdose of pills. This shocking incident leaves Marcus fearful of his home environment, leading him to shadow Will, hoping to uncover some semblance of stability in the young bachelor’s life. He swiftly discovers that Will is not the devoted father he pretended to be, which culminates in Marcus attempting to blackmail Will into dating his mother, believing that a romantic relationship could alleviate her chronic unhappiness. When this plan crumbles, Marcus simply starts spending more time at Will’s apartment, much to the latter's initial annoyance.
As the days pass in a monotone haze, they take a sudden turn when Marcus is chased by bullies to Will's refuge. This encounter forces Will to recognize the significant role he has begun to play in Marcus's life. Determined to help Marcus navigate the rough waters of adolescence, Will takes him shopping for new shoes—only for them to be stolen shortly thereafter. The incident fuels a heated exchange among Marcus, Fiona, and Will, unraveling tensions that have been building.
At school, Marcus finds companionship in an eccentric Goth girl named Ellie (Natalia Tena) and develops a burgeoning crush on her. Simultaneously, Will finds himself infatuated with the single mother, Rachel (Rachel Weisz). In a bid to attract Rachel’s attention, Will fabricates a façade in which he presents Marcus as his son. During a conversation, the contrast between a friend and a girlfriend becomes a topic of curiosity for Marcus, prompting him to reflect that intimacy matters less to him than connection and companionship.
As events reach a dramatic conflict, Will eventually confesses to Rachel about Marcus not being his biological son, resulting in a painful breakup. Meanwhile, Marcus comes home one day to find Fiona in tears, desiring to unload his burdens to Will, who remains emotionally inaccessible, still harping on his lost romance with Rachel. In a moment of desperation, Marcus resolves to perform at the school variety show—a decision deemed “suicidal” by Ellie, but one he believes could bring joy to Fiona.
Despite continuing his superficial lifestyle, Will starts to feel an emptiness that echoes deep within. He acknowledges that “there was only one thing that meant something to me: Marcus.” After a fateful SPAT meeting, he rushes to Fiona, imploring her not to attempt suicide again, only to learn about Marcus's plans to sing. They both hastily head to the school event, where Will finds Rachel in attendance. Just as he tries to halt Marcus, who insists on singing for his mother’s happiness, the young boy delivers a comically off-key rendition of “Killing Me Softly.”
When the audience begins to mock him, Will emerges on stage with a guitar, supporting Marcus's performance. Together they turn the tables, receiving moderate applause that eventually transitions into a memorable moment for the kids attending. As the performance wraps up, Will engages in an improvised solo, selfishly attempting to overshadow Marcus, changing the narrative of that unforgettable day.
The film lovingly culminates at the following year's Christmas gathering at Will's residence, where a shy but lively group comprises Marcus, Rachel, her son Ali, Fiona, and even Ellie. Here, the character undergoes a remarkable transformation, evolving his earlier belief that “Every man is an island.” Now, he recognizes, “clearly, some men are part of island chains.” The mention of a potential marriage to Rachel hangs in the air, and Marcus shares his perceptive insight that couples alone cannot define the future; the significance lies in the support system they build together, emphasizing the words of Jon Bon Jovi: “No man is an island.”
