The story revolves around Daniel Brennan, a deaf man recently released from prison, who seeks to uncover the truth behind the events that led to his imprisonment. Central mysteries include the historic sexual abuse at Hawthorne Park school by the headmaster Jim Monroe, the true circumstances of Ray's death, and the complex relationships and betrayals among the characters connected to these events.

The series explores how the characters, especially Daniel and his old school friends, have buried traumatic memories of sexual abuse by the headmaster Jim Monroe. These repressed memories resurface, affecting their present lives deeply. Daniel's quest to confront Monroe and the emotional toll on the survivors are key elements, highlighting themes of trauma, survival, and the struggle for justice.

Daniel Brennan's deafness is integral to the narrative, shaping his experiences and interactions. The series is notable for its inclusive storytelling, featuring a majority deaf cast and use of British Sign Language alongside spoken English. Daniel's perspective as a deaf man seeking truth and redemption adds a unique sensory and emotional dimension to the story.

Key relationships include Daniel's strained ties with family and friends due to his imprisonment, the friendship and shared trauma with Ray and Sean, and the complex dynamics involving Christine and other characters connected to the school and abuse scandal. Conflicts arise from betrayal, secrets, and the pursuit of justice, driving much of the emotional tension in the series.

Reunion is described as an emotional thriller of revenge and redemption, focusing on Daniel's determination to uncover the truth and seek closure. His actions, including confronting past abuses and the people involved, reflect a journey toward personal and collective redemption. The narrative balances the pain of past wrongs with the hope for healing and justice.