On her first day as a newly qualified teacher in a Category B prison, Kate Stuart meets Michael and is immediately struck by his uncanny resemblance to her son. Michael is shy and unmotivated in class, so Kate encourages him to write about his life prior to his murder conviction. His writing reveals a lifetime of abuse and disillusionment, and this stirs up memories from Kate's own life.

When Michael falls into depression and attempts suicide, Kate believes she is to blame for asking him to revisit his past. On his return to class after a stay in hospital, Michael continues to write, but Kate soon realises that the now sexually explicit content of his letters is intended to arouse her. Her obsession with the young prisoner's welfare makes her oblivious to what is happening closer to home—her son's drug addiction and husband's affair.