Prem Sharma and his wife Kamini await the arrival of his formidable mother-in-law, Pushpa who is paying a visit.

Trefelin is deserted as Prem waits for a vaccination unit to arrive from Cardiff. But Reverend Todd is still determined that only he can save the village, and wastes no time in telling the villagers that God has stepped in where Prem's medicine has failed. The community seems oblivious to the deadly outbreak that it faces, and Prem seems to be losing the fight.

With Trefelin under quarantine, supplies are getting low. Despite Prem's attempts to piece together the evidence, the real source of the outbreak is still unknown. As one by one the miners who played cards in Ceri's barn fall victim to the virus, it seems that Dan knows more than he is letting on about how he fell ill.

Reporters gather at the surgery to hear that the outbreak of smallpox in Trefelin is finally under control. But Prem is not convinced that they have managed to locate the real source of the disease, and so the village is still not safe.