Meet Tilly Mahoney, a woman with three notable characteristics: she's a notorious liar, secretly adores her best friend, and is concocting a dubious scheme to sabotage his impending nuptials. Tilly's world capsizes when her lifelong confidant and pillar of support proposes to another, catapulting her into a mission to dismantle the wedding. Enter Zack, the brooding ex-boyfriend of the bride, who becomes Tilly's unlikely ally. As the two partners-in-crime channel their efforts into a series of mishaps to thwart the ceremony, Tilly's convictions uncannily start to waver. Juggling the chaos of the plot and a burgeoning friendship with Zack, Tilly begins to question her perception of love, loyalty, and whether the smiles she now cherishes were right in front of her all along.