On holiday in Cornwall, the gymnastics school teacher Caroline Trewella encounters a striking doppelgänger who shares her exact appearance—her distant mermaid relative, Miranda. The two form a startling bond, and Miranda proposes a bold swap: Caroline will let Miranda take her place for a seaside break while Caroline heads off on a cycling excursion with a friend. To make the plan work, Caroline pretends to have an accident that will require a wheelchair for a few weeks, a ruse that softly masks Miranda’s unusual tail and aquatic nature. Into this arrangement enters Nurse Carey, who knows about Miranda and was even part of the previous film, hired to attend Miranda and keep the deception intact.
Caroline is engaged to Ronald Baker, but Miranda disapproves of him from the start. Seizing the chance to improve Caroline’s prospects, Miranda flirts openly with two eligible bachelors, Jeff Saunders and Colonel Barclay Sutton, right under Ronald’s nose. When Ronald reveals his work in the government sanitation department and his supportive stance on dumping garbage into the ocean, Miranda wastes no time in delivering a decisive rebuke—dousing him with a tureen of cold soup. The moment highlights Miranda’s sharp, fearless wit and her stubborn preference for a more exciting, compatible match for Caroline.
Meanwhile, Barbara Davenport, Barclay’s fiancée, instantly distrusts Miranda and quickly uncovers the secret behind Caroline’s sudden disappearance. She hatches a plan to lure Caroline back by arranging for Miranda to perform at a charity concert, hoping to expose the disguise and reclaim her own engagement. Caroline, upon reading about the concert, senses the trap and returns abruptly to reclaim her life, outsmarting Barbara and thwarting the scheme.
As the holiday drama unfolds, the two men intrigue Caroline anew. Jeff Saunders takes Caroline out on a boating outing, and the course of romance takes a delicate turn: he leans in to kiss her, she initially resists, then allows the moment to unfold, guided by a mix of curiosity and genuine feeling. All the while, a regretful Miranda watches the scene, quietly mourning the loss of the life she briefly stole from Caroline even as the bond between the two grows stronger.
Across the waves and shorelines, the film delves into friendship, identity, and the playful tensions of mistaken appearances. The Cornwall setting—with its windy cliffs, tranquil harbors, and sunlit mornings—frames a tale that blends light comedy with a gentle meditation on longing and belonging. As the sun sets on this curious swap, Caroline and Miranda navigate borders of love, loyalty, and self-discovery, leaving the audience with a nuanced sense of how far one might go for a chance at a better match, and what it means to choose a life that truly feels like home.
