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.

Cathy's triumph at CeCe's turns dark when a club manager is found dead and Alphy is discovered drunk at an illegal poker game. As Geordie uncovers a web of extortion, friendships fracture and faith falters. Leonard finds hope in caring for young Raymond.