Sidney receives a series of anonymous phone calls, which he realises may be linked to a series of murders in which the victims were all important community figures killed by someone who leaves dead birds as a grisly calling card. The threat forces Sidney to question whether he can reconcile his relationship with Amanda and his calling as a vicar. Leonard bonds with Hilary as she cares for her dying father, while Geordie's investigation of the killings leads him to a mysterious home for people with disabilities.
Sidney and Geordie join a local cricket team to play a match against nearby Whittlesford, but team captain Geoff Towler (Peter Davison) seems to have an objection to talented young Pakistani batsman Zafar, and is even willing to forfeit the game to spite the player. After the match, a buffet ends badly when contaminated beer leaves everyone feeling ill, a matter Geoff is keen for Geordie to cover up. However, a worse fate awaits Zafar, who is later found to have received a fatal dose of the poison his teammates and spectators had received.
Leonard gets caught up in an armed robbery at the village post office, and manages to identify the masked culprit. Geordie takes no chances when going to arrest the criminal, who has a record of similarly unhappy crimes - but is surprised to discover that the suspect has been cuddled. Meanwhile, a second robbery occurs, carried out by a man and a woman who have adopted the dead robber's trademark of disguising himself with a gas mask. Back at the Vicarage, the atmosphere is tense between Sidney and Amanda.
A factory worker dies in what appears to be a drunken accident, but Geordie suspects foul play. However, secret forces are determined to shut down his investigation. Mrs Maguire is confronted by a face from the past, while Sidney wrestles with his conscience, as his feelings for Amanda clash with his sense of duty - leading to accusations of hypocrisy from Leonard.
Sidney tries to put his life in Grantchester behind him by going in search of the man who stole Mrs Maguire's life savings, and ends up finding a new home in a travellers' community. However, he falls under suspicions when a hug rocks the camp. Geordie tracks his friend down and together they set out to solve the mystery - and hopefully give Sidney a sense of purpose in his life.
On a Sunday morning in Grantchester, Sidney visits the Archdeacon to discuss his resignation. Sidney has lost his faith in a church that won't allow him to be married to the woman he loves. With a heavy heart the Archdeacon tells Sidney he must go away and write a resignation letter in order to make it official.