While Louisa begins to make arrangements for the wedding it's business as usual for the doctor. He's puzzled about why Beth Sawle's knee replacement wound is not responding to the treatment he's prescribed, and has become infected. He decides to visit her in the remote cottage she shares with her strange sister, Janet.

The doctor discovers Janet has been refusing to allow Beth to take the antibiotics the doctor has given her. She insists a potion she has made from mushrooms growing in the cellar of their house is a much more effective and natural method of treatment.

But on an inspection of the cellar the doctor discovers the mushrooms are also the cause of an outbreak of disease in the village. Bert Large, Postman Dave and restaurant chef, Mick Mabley, are among the victims.
Bert Large's ill health is not his only problem. His restaurant is in financial trouble. To cut costs he cancels the vegetable order with Aunt Joan, to her fury. Son Al decides it is time to take action to save the business.