Martin Clunes returns as the grumpy GP of sleepy Portwenn in this new series. Dr Ellingham visits an elderly patient in the village - but ends up having to contend with her irate son. To make matters worse the lad turns out to be one of Louisa's ex-boyfriends. However, trouble is not just confined to the doctor's daily routine as the rest of the community must deal with the threat of a mystery mugger.
An outbreak of what the Doc suspects is Impetigo leads to problems for Louisa, who must decide whether to follow the Doc's orders to force the infected children to stay at home, or to help the parents by allowing the children to attend school. The decision is made harder by her impending interview to take over the job of Head Teacher - in front of a board of governors that (to his surprise) includes Doc Martin.
Al discovers that Bert may not be his father and goes in search of the truth. An odd family with a lack of hygiene and a passion for taxidermy contract salmonella poisoning, but Martin has difficulty convincing them to accept treatment. PC Mylow's bossy sister arrives in Portwenn and sets up a herbalist business in his flat. However, when her remedies increase his patients' many ailments the doctor is forced to take action.
The people of Portwenn are concerned for Radio Portwenn's DJ Caroline Bosman, whose increasingly erratic behaviour has them suspecting that she has been hitting the bottle. The Doc has to deal with an elderly patient whose personal aroma can clear a room, but is unable to determine a medical cause for the stench. PC Mylow hopes that his pheremone spray will endear him to a pretty newcomer to the village, while the Doc/Louisa/Danny triangle gets even more complicated.
Pauline is all set to achieve her ambition when she is given the chance to join the Portwenn Lifeboat Crew. However, her joy is short-lived when she discovers the chauvinistic tendencies of her shipmates. Martin is accused of hug by the husband of a woman who died in his care. The irate man resorts to sabotaging Aunt Joan's crops in retaliation but an unexpected twist reveals the true motivation for his ire.
Martin is surprised when his parents visit out of the blue, but they bring unwelcome tidings for all, especially Aunt Joan, who may be driven out of her home. School secretary Maureen receives better news when her thyroid problem turns out to be a pregnancy. Louisa calls the doctor when Danny collapses - but the ambulance is delayed and Ellingham must perform emergency surgery to save his life.
Mark has an unusual idea for a stag night, which involves camping under the stars rather than going to the pub. However, the jaunt ends in disaster when he gets lost in the woods and then bitten by a snake, leaving Martin with the task of locating the clueless copper and saving his marriage before it has begun.
Meanwhile, the teenagers of Portwenn provoke the wrath of the doctor by inventing a deadly game that threatens one boy's life when he has an allergic reaction to a weever fish sting.
Mark is forced to investigate his fiancee's past when a stranger arrives in the village with a mysterious photo. Mrs Tishell finally removes the neck collar she has worn for years, and suffers a prolapsed disc as a result. Martin reveals his true feelings for Louisa over a few glasses of wine, but he drinks too much and wakes the next morning to a waiting room full of giggling patients, a raging hangover and a distinct feeling of uneasiness.