Siyeon, a professional assassin, vows to avoid men following a betrayal by his ex-lover. However, his stance wavers when he occupies a luxurious penthouse belonging to Taekyung, a charming heir with hidden depths. Beyond Taekyung's playboy image lies a complex individual, just as Siyeon's composed demeanor masks a layered personality. Despite their mutual confusion, an inexplicable attraction sparks between them, leaving both puzzled by their undeniable connection.