In a bustling New York apartment, Maisie (Onata Aprile), a perceptive six-year-old, weaves through the chaotic lives of her parents, Susanna (Julianne Moore), a passionate singer in a rock band, and Beale (Steve Coogan), an international art dealer entrenched in the elite world of art. The regular bickering and fierce arguments between the couple leave poor Maisie feeling invisible and devoid of emotional support, causing her to turn to their compassionate nanny, Margo (Joanna Vanderham).
Despite her tender age, Maisie starts to comprehend the nuances of her parents' chaotic relationship. This is highlighted when Susanna makes a desperate attempt to shield herself by changing the apartment's lock, effectively locking Beale out. As tensions rise, the family dynamic is thrown into disarray when Susanna and Beale decide to separate, which leads to a challenging joint custody arrangement for Maisie.
In their quest for autonomy, Margo moves into Beale's apartment, where they swiftly marry, prompting Susanna to make a rash choice by marrying Lincoln (Alexander Skarsgård), a bartender she barely knows. To everyone’s surprise, Maisie develops an unexpected connection with Lincoln, though it only intensifies Susanna's growing jealousy towards the affection her daughter shows him.
As the adults become increasingly self-involved with their battles over custody and personal vendettas, Maisie finds herself stuck in the crossfire, shuttling between her parents' homes. During this time, Margo and Lincoln emerge as her primary caregivers, especially when Susanna goes on tour and Beale is frequently away on business trips. Discontent with the disintegration of his relationship with Margo, Beale finally decides to move to the United Kingdom, further complicating the situation.
With Beale and Susanna largely absent, a new bond begins to blossom between Margo, Lincoln, and Maisie. However, their serene life is abruptly interrupted when they encounter Susanna in New York. This leads to a volatile confrontation where Susanna accuses Lincoln and Margo of "stealing" her daughter. In a moment of clarity, Lincoln asserts that their relationship has come to an end, firmly telling Susanna that she no longer deserves Maisie's affection.
When Susanna leaves the city, Maisie returns to Margo's care. Margo seizes the moment to invite Lincoln to her cousin's beach house, which fills Maisie with joy. As they enjoy their time together, a spark ignites between Margo and Lincoln. However, tensions flare anew when Susanna shows up unannounced at the beach house in her tour bus, attempting to reclaim her daughter. Yet, to everyone's surprise, Maisie chooses to stay with Margo and Lincoln, ultimately compelling Susanna to confront the reality that her daughter feels a sense of fear towards her, leading her to accept that it is indeed in Maisie's best interest to remain behind.
