It wasn't long ago that Calvin Weir-Fields (Paul Dano) was a literary wunderkind with an acclaimed first novel. But since then, he's been stricken with a stubborn case of writer's block magnified by a dismal love life. In a last-ditch attempt to reignite his creative spark, Calvin begins to envision a female protagonist in his mind. Her name is Ruby Sparks (Zoe Kazan) and from the minute he imagines her, he feels creatively invigorated to write about her. Until she shows up in his living room. Is this a joke, a sign of madness, an act of magic? Whatever it is, it feels incredible. Suddenly, Ruby is sleeping in Calvin's bed, cooking in his kitchen, beguiling him in every way, with one mind-boggling twist: he somehow has the power to change her every time he sits at his typewriter. As Calvin tries to juggle this power, he faces a major dilemma as a writer and a boyfriend: what will it take to make this relationship from his imagination work in the real world?