Pablo is a young, wealthy but solitary man traumatized by a fatal car accident. He meets Lara through a dating app tied to an exchange of the titular blue box. As their relationship grows, Lara draws Pablo out of his shell. But an anonymous warning alerts Pablo that Lara may not be all that she seems. What begins as an intimate connection gradually turns into a tense psychological game of cat and mouse, forcing Pablo to confront both his past and the true nature of the woman he is falling in love with.
