On his birthday, Alexander (10 years old) promises his grandmother that he will never fall in love, lest he suffer his father’s fate. Every Sunday, Alexander visits his father who lives underground near the Vienna subway. A few years later, Alexander also moves underground during the day, being employed at the lost property office. There he meets the beautiful Caro, who owns a small hat shop in the subway. Although Alexander has managed to avoid love up to that point, his self-imposed vow will find its end and he will begin a bittersweet journey where he will turn summer into winter and understand that love is not about winning, it is about to take risks.