An old mixtape vanishes from the school radio room, a transfer boy hears Nessa's locker number on the tape, and a hidden clue pulls them into a love story her mother never finished. A missing cassette should have been nothing more than a school mystery. But when Nessa finds an old tape gone from the radio-room archive, the only clue points to her locker and a quiet transfer boy who already heard what was hidden on it. The voice on the recording is older than both of them. The message should not know her name, her number, or anything about the life she is living now. Yet it does. As Nessa and Roman follow the trail through dusty booth cabinets, attic secrets, forgotten photographs, and a school room that seems to remember everything, the mystery stops feeling like history and starts feeling personal. What begins as a search for a missing mixtape turns into the buried story of a first love, a silence that lasted too long, and a room that refuses to let the truth stay hidden forever. Set against the warm glow of school hallways, old songs, and the fragile courage of speaking honestly before it is graceful, Side B Secret is a clean YA romance with nostalgia, emotional depth, and a hidden clue at its heart. It is a story about voices, rooms, memory, and the terrifying sweetness of realizing the truth is louder when one person begins to matter more than the rest of the room.