Filmed in 1977, the opening credit sequence for the first three series feature Siegfried and James driving around the Dales and, at one point, sharing a laugh in the car.
James treats Phineas Calvert's cow, which has developed sunstroke, and decides - under the watch of the difficult Mr Soames - to euthanise Lord Hulton's valuable horse after he diagnoses that it is too far gone with an agonising torsion.
James picks up Siegfried's brother Tristan from the station upon his return from veterinary college in Edinburgh, having failed pathology and parasitology.
James exacts revenge by calling Tristan, pretending to be the farmer whose calf bed the duo put back in earlier in the day, saying the same thing has happened again.
On a call to her father's Heston Grange farm in Ellsdale to treat a calf with a fractured leg, James meets Helen Alderson for the first time since they were on the bus together.
He arranges a double date at a dance, with local girls Connie and Brenda, but things take a turn for the worse when Helen shows up with Richard Edmundson.
James is finally beginning to make real progress with Helen, who invites him to Sunday tea at the Aldersons', but ends up treating one of their cows that falls ill.
Mrs Dalby is worried about her cattle, and James struggles to find a diagnosis until he realises that the cows have rings around their eyes, as if they are wearing spectacles.
The vets and the village doctor, who has set up practice next door to Skeldale, see an opportunity to teach Gobber Newhouse, a locally bully and wife-beater, a lesson when he steps on a rusty nail.
James has to deal with Mrs Donovan, a self-educated animal healer whose dog is killed in an accident, and with Angus Grier, who has a broken arm.
He offers to give them a lift back to Darrowby to attend a performance of Handel's Messiah at the church, but the family's lunch appears interminable.
James also has to treat Tim Alton's prize pig who has gone off her feed, the Taverners' dog, Dilly, and he faces a dilemma when Mrs Tompkins' budgerigar dies in his care.
Guest appearance: Norah Fulton (as Mrs Horner), Gorden Kaye (as Kit Bilton) James has to deal with a difficult calving.
Mr Biggins tells James about his cowhand, Ned Finch, who goes drinking every night and is drawn to the bright lights of "big city" Briston.
War is becoming a distinct possibility, so Helen stocks up on food, while Tristan, at the request of his brother, puts tape on the windows in an attempt to minimise the chance of them shattering if the bombs arrive.
"Though one of my favourite ones — because it was so true, I think — was my scene with Peter when war is declared, and we were sat at the top of a ridge, looking around at this wonderful Yorkshire countryside.
Siegfried decides the time has come to hire a full-time assistant, and Calum Buchanan, with whom Tristan attended veterinary school in Edinburgh, fits the bill.
Lionel Brough decides to buy a pig farm, but runs into problems when his stock falls ill with what James suspects is swine fever.
The vets have to deal with an outbreak of fleas and are busy preparing for a bank holiday event intended to raise money for a new church roof.
Siegfried is thinking of changing his drugs rep, until the current one, Mr Barge, helps to cure a nasty case of white scour.
Calum cooks a meal for James and Siegfried, but it takes so long to prepare that his guests have drunk too much and decide to go to the kitchen to see how it's coming on.
After experiencing the resistance of local farmers to female vets, and realising that Calum is getting too keen on her, Emma decides to return home.
The opening credits hark back to that of the first run, with Siegfried driving the car and James being the passenger in an excerpt from the episode "The Rough and the Smooth".
The opening credit sequence of the early episodes of the final series again features Siegfried and James driving around the Dales, this time from head-on rather than from the driver's side of the vehicle.
The closing credits sequences are changed later in the series, with James exiting the back of Skeldale House and being roped into assisting Siegfried in working on the latter's car.
After two years in Ireland, Tristan returns to Darrowby and promptly falls victim of James' practical joke which leaves him intent on avoiding Susie Parker at all costs.
While she is lost, Siegfried tells James and Tristan that it is time — with no concern about cost — to expand the surgery to include an observatory wing; when Prudence is found, however, he conveniently forgets all about it.
Characters: Mrs Pumphrey, Hodgekin, Ewan Ross, Henry Clintock, Harold Peart, Mr Lupton, Silas Wenlow.
Convinced that he is purposely being given all the difficult jobs, he insists Siegfried swap rounds for the day, including a pig which he suspects is a family pet.
But when he's also asked to castrate its litter of piglets, his careless disposal of the 'cut-offs' full of anaesthetic leads to the numerous farm cats eating them and passing out.