Rivalry turns deadly when a Cambridge quiz team member is found dead and Alphy's Bible turns up at the scene. As Geordie jumps to conclusions, Alphy uncovers a dark world of bullying, secrecy, and shame. Meanwhile, Mira's role in his life leaves Alphy questioning love, identity, and faith, while Geordie faces a decision that could divide them forever.

Alphy's trip to reconcile with his mother takes a shocking turn when he is introduced to someone and uncovers painful truths about family and faith. On the train home, a fellow passenger is murdered, and Alphy becomes the prime suspect amid prejudice and fear. Back in Grantchester, Leonard defends troubled Raymond from Geordie, and Miss Scott hides a big secret.