Cassandra follows Seymour, a non-verbal autistic musician whose voice comes to life through his autoharp. When his longtime support worker, Cassandra, unexpectedly leaves, Seymour is thrust into a new chapter of independence and self-discovery. Enter Michael, a new support worker who challenges Seymour's world. Michael encourages Seymour to step out of his comfort zone, involving him in concerts and band practices, and offering him the chance to perform in front of audiences for the first time. This new exposure to the wider music scene becomes a transformative experience, unlocking Seymour's potential and giving him the opportunity to share his powerful, unique music with the world. However, Seymour's fiercely protective mother, Nina, remains unaware of the changes in his life. As Michael pushes Seymour toward new experiences, Nina's growing concerns about her son's well-being lead to mounting tensions with Michael, threatening the fragile balance of Seymour's newfound independence. As their worlds collide, Seymour must navigate the shifting dynamics of family, trust, and his own identity, all while embracing his place in the music world. Cassandra is a moving exploration of the power of art, the complexities of relationships, and the journey to find one's voice in a world that often doesn't listen.