Dr Martin Ellingham (Martin Clunes), a brilliant and successful vascular surgeon at Imperial College London, develops haemophobia – a fear of blood, forcing him to stop practising surgery.
He obtains a post as the sole general practitioner (GP) in the sleepy Cornish village of Portwenn, where he had spent childhood holidays with his Aunt Joan (Stephanie Cole), who owns a local farm.
Upon arriving in Portwenn – where, to his frustration, the locals address him as "Doc Martin" – he finds the surgery in chaos and inherits an incompetent receptionist, Elaine Denham (Lucy Punch).
In series 2–4, she is replaced by Pauline Lamb (Katherine Parkinson), a new receptionist, and later also a phlebotomist.
In Series 5, Morwenna Newcross (Jessica Ransom) takes up the post.

The programme revolves around Ellingham's interactions with the local Cornish villagers.
Despite his medical excellence, Ellingham is grouchy, abrupt, and lacks social skills.
His direct, emotionless manner offends many of the villagers, made worse by his invariably unpleasant responses to their ignorant, often foolish, comments.
They perceive him to be hot-tempered and lacking in a bedside manner, whereas he feels he is performing his duties in a professional and by-the-book manner, not wasting time chatting.
Ellingham is very deadpan and dresses formally in a business suit and tie, regardless of the weather or the occasion, and he never takes off his jacket, even when delivering babies.
He does not smoke and has no hesitation in pointing out the risks of unhealthy behaviours, both in private and in public gatherings.

The villagers eventually discover his fear of blood, and the frequent and debilitating bouts of nausea and vomiting it causes.
In spite of this handicap, Ellingham proves to be an expert diagnostician and responds effectively to various emergencies in his medical practice; thus, he gradually gains grudging respect from his neighbours.

Ellingham does not get on with his parents, but has a warm relationship with his aunt, Joan Norton (Stephanie Cole), who provides emotional support.
When she dies after a heart attack, her sister Ruth (Eileen Atkins), a retired psychiatrist, comes to Portwenn to take care of her affairs, and eventually decides to use the village as a permanent retreat, offering Martin the support Joan had provided.

A major theme through the series is Ellingham's relationship with primary school teacher Louisa Glasson (Caroline Catz).
Due to his difficulty in expressing feelings and his insensitive nature, the relationship has many ups and downs; though they eventually have a child and later marry.

Other series regulars are father and son Bert and Al Large who are always trying to run a small business of some type; pharmacist Sally Tishell who is infatuated with Martin; and Mark Mylow, a quirky police officer who is replaced in series 3 by the bumbling Joe Penhale.

Regular cast members have characterised Ellingham's personality thus:
Joe Absolom: "The Doctor is ... slightly autistic, probably, on the spectrum."

Martin Clunes: "Lots of people say that he is Aspergic or something to some degree—which yes, I think he is."
He has also said, "He's clearly wired the way he's wired, but growing up being loathed by both your parents is going to leave a footprint.
That's why he's so dysfunctional with relationships, 'cause there's gaps in his makeup.
There's a sad little boy in there that comes out a lot, and that's what a lot of that frowning is."

Eileen Atkins: "He's unable to connect with people.
He just can't understand why people can't just take the truth, in a rather rough manner.
If your parents have been very cold towards you and just factual, then that's very hard for you to grow up being—'loving' is too strong a word—an affectionate person."
Dr Martin Ellingham (Martin Clunes), a brilliant and successful vascular surgeon at Imperial College London, develops haemophobia – a fear of blood, forcing him to stop practising surgery. He obtains a post as the sole general practitioner (GP) in the sleepy Cornish village of Portwenn, where he had spent childhood holidays with his Aunt Joan (Stephanie Cole), who owns a local farm. Upon arriving in Portwenn – where, to his frustration, the locals address him as "Doc Martin" – he finds the surgery in chaos and inherits an incompetent receptionist, Elaine Denham (Lucy Punch). In series 2–4, she is replaced by Pauline Lamb (Katherine Parkinson), a new receptionist, and later also a phlebotomist. In Series 5, Morwenna Newcross (Jessica Ransom) takes up the post.
The programme revolves around Ellingham's interactions with the local Cornish villagers. Despite his medical excellence, Ellingham is grouchy, abrupt, and lacks social skills. His direct, emotionless manner offends many of the villagers, made worse by his invariably unpleasant responses to their ignorant, often foolish, comments. They perceive him to be hot-tempered and lacking in a bedside manner, whereas he feels he is performing his duties in a professional and by-the-book manner, not wasting time chatting. Ellingham is very deadpan and dresses formally in a business suit and tie, regardless of the weather or the occasion, and he never takes off his jacket, even when delivering babies. He does not smoke and has no hesitation in pointing out the risks of unhealthy behaviours, both in private and in public gatherings. 
The villagers eventually discover his fear of blood, and the frequent and debilitating bouts of nausea and vomiting it causes. In spite of this handicap, Ellingham proves to be an expert diagnostician and responds effectively to various emergencies in his medical practice; thus, he gradually gains grudging respect from his neighbours. 
Ellingham does not get on with his parents, but has a warm relationship with his aunt, Joan Norton (Stephanie Cole), who provides emotional support. When she dies after a heart attack, her sister Ruth (Eileen Atkins), a retired psychiatrist, comes to Portwenn to take care of her affairs, and eventually decides to use the village as a permanent retreat, offering Martin the support Joan had provided.
A major theme through the series is Ellingham's relationship with primary school teacher Louisa Glasson (Caroline Catz). Due to his difficulty in expressing feelings and his insensitive nature, the relationship has many ups and downs; though they eventually have a child and later marry.
Other series regulars are father and son Bert and Al Large who are always trying to run a small business of some type; pharmacist Sally Tishell who is infatuated with Martin; and Mark Mylow, a quirky police officer who is replaced in series 3 by the bumbling Joe Penhale.
Regular cast members have characterised Ellingham's personality thus:
Joe Absolom: "The Doctor is ... slightly autistic, probably, on the spectrum."
Martin Clunes: "Lots of people say that he is Aspergic or something to some degree—which yes, I think he is." He has also said, "He's clearly wired the way he's wired, but growing up being loathed by both your parents is going to leave a footprint. That's why he's so dysfunctional with relationships, 'cause there's gaps in his makeup. There's a sad little boy in there that comes out a lot, and that's what a lot of that frowning is."
Eileen Atkins: "He's unable to connect with people. He just can't understand why people can't just take the truth, in a rather rough manner. If your parents have been very cold towards you and just factual, then that's very hard for you to grow up being—'loving' is too strong a word—an affectionate person."
Doc Martin