The film opens with Julie, a character depicted by the talented Juliet Berto, seated on a park bench engrossed in a fascinating book filled with magic spells. As she is lost in her reading, she notices a mysterious woman named Céline, played by the remarkable Bulle Ogier, who ambles by, dropping various items in her path, reminiscent of Lewis Carroll's White Rabbit. Intrigued, Julie begins to collect Céline's belongings and embarks on a whimsical adventure across Paris, at times racing up the enchanting streets, such as the iconic Montmartre, to keep up with Céline's tram.
As their paths intertwine through the picturesque Parisian scenery, the relationship between Julie and Céline deepens. After a series of escapades that momentarily separate them, Céline makes a decision to move in with Julie. This development leads to amusing instances of identity swapping; for instance, Céline poses as Julie to charm the latter's childhood sweetheart, while Julie takes on Céline's role during a cabaret audition.
In the latter half of the narrative, the focus shifts to their visits to an enigmatic location: 7 bis, rue du Nadir-aux-Pommes, a mansion shrouded in mystery, nestled within private, tranquil grounds of Paris. Initially appearing to be uninhabited and forgotten, this house becomes significant as Céline uncovers her past connection as a nanny for a complicated family—comprising two envious sisters, a widowed father, and a frail child. A curious and repetitive cycle ensues: whenever either woman steps inside the mansion, they vanish only to reappear later, bewildered, having lost all memory of their time spent in the house. Each time they return via taxi, they discover a peculiar candy lodged in their mouths—an item that appears to hold great significance. This candy soon becomes a key, propelling them back into an alternate reality filled with whimsical twists and turns, echoing elements of both Lewis Carroll's fantastical world and Marcel Proust's madeleine.
As the story unfolds, the women grapple with unraveling the central enigma of the mansion, which harbors a dark secret: amidst a web of jealousy surrounding the widower's affections, the tragic murder of a young child casts a shadow. The narrative unfolds like a meticulously rehearsed stage play, rich with repeated phrases that the duo soon learns to navigate with humor and familiarity. With each taste of the candy, they glean more insights into the day's happenings. Instead of remaining passive recipients of the story, they realize their potential to interact with the unfolding narrative, actively shaping its direction.
So, as the plot unspools with its mechanical precision, Julie and Céline seize the reins of the story, transforming it into an interactive experience. They inject new dialogue and weave diverse actions into the fabric of the events within the house. In an extraordinary act of creativity, they shift the narrative's conclusion, ultimately saving the young girl who had met a grim fate. As both dimensions of reality converge, the duo, after liberating the girl from her fate within this House of Fiction, find themselves transported back to Julie's apartment, where they are unexpectedly joined by Madlyn, the young girl, now safe and sound in 1970s Paris.
To unwind from their exhilarating adventure, Céline, Julie, and Madlyn take a serene rowboat ride on a calm river, gliding peacefully along the water. However, an uncanny feeling lingers in the air as they fall silent upon witnessing another boat passing swiftly by. This vessel carries figures from the house of another time, a haunting reminder that the alternate reality has trailed them back home. Yet, Céline, Julie, and Madlyn perceive these apparitions as mere antiquated props, suspended in time.
The film closes with a poignant image of Céline, who, lulled into a dreamy state on a park bench, glimpses Julie rushing by as she drops her magic book in her typical White Rabbit fashion. Picking it up, Céline is compelled to chase after Julie, thus weaving together their extraordinary fates in a delightful blend of reality and fantasy.