This third series of Doc Martin continues to have a mixed critical reaction. Some love it, finding that the gentle story of the Cornish village doctor (played by Martin Clunes) and his on-off romance with local headmistress Louisa Glasson (Caroline Catz) is top-notch, while others find the doctor is dull, and the show lacks strong plots and genuine humour. One thing's for certain - the programme is pulling big audiences. On average around eight million viewers are tuning in each week.

In tonight's penultimate episode of the current series, Portwenn is buzzing with the news of the engagement of Doc Martin (Clunes) and headmistress Louisa (Catz). Aunt Joan (Stephanie Cole) is disappointed that she has to hear about the pending nuptials from village postman Dave (Tony Maudsley), rather from her own nephew. But she's pleased that the couple are together at long last.

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 (Thelma Barlow) 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 (Irene Sutcliffe).

The doctor's arrival is far from welcomed by Janet who appears to have no faith in conventional medicine. 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 aspergillosis in the village. Bert Large (Ian McNeice), Postman Dave and restaurant chef Mick Mabley (Joseph Morgan) 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 (Joe Absolom) decides it is time to take action to save the business...