England is at war and the time has come for James and Siegfried to join their military units. Their last day at the practice is a busy one and James is repeatedly called out when he had hopes to spend a last, quiet evening at home with Helen. Siegfried surprises James with a small gift. Mrs. Hall also has a surprise announcement for everyone and Tristan receives shocking news from the Royal College of Veterinary Surgeons.

Siegfried discovers that a gift given in good faith has brought the deadly foot-and-mouth disease to the dales, and James accidentally hits upon a "sleep cure" for Mrs. Flaxton's poodle.

James' temper is fraying fast -- what with two car accidents in the space of a week, an inauspicious meeting with Helen's family and his rival still lurking around Helen like a "big glossy spider".

The fortunes of the hard-working Dalby family look set to dwindle even further until almost by accident James discovers the cause of their herd's illness. However, James still needs a push start on other fronts, and Siegfried and Tristan decide to remedy matters with their own expert advice.

Having failed his exams, Tristan fears his brother's wrath. In a desperate effort to reform, Tristan shuns cigarettes, alcohol and women and adopts a rigorous routine of dawn runs and hard work.

Siegfried bumps into Mr. Beresford, the manager of the local bank whose dog behaves badly in the car. Tristan woos the lovely Marjorie Simpson and Siegfried meets Sarah Raworth. James treats the elderly Mr. Bailey's dog who has developed a bad case of bronchitis and Siegfried criticizes James when he waives the fee. Siegfried, however, has trouble following his own advice. Tristan rescues a severely injured cat and then convinces James to treat him rather than put him down. Helen promptly adopts him and nurses him back to good health but is devastated when she learns the cat belongs to the Gibbons family. Everyone celebrates Tristan's birthday.

Tristan has had a rather late night and Siegfried takes him to task over his bad habits. Tristan announces that he has a steady girlfriend, Deborah Mount and will reform his wild ways. Turns out Deborah's father doesn't know anything about the relationship and may not approve. When he does hear of it, he has serious doubts about Tristan's character. Tristan doesn't help his case with his silly pranks. James has several encounters with a street urchin, Wesley Binks, whom he'd earlier caught stealing. James nonetheless helps Wesley out when his dog contracts distemper. Siegfried reacts badly when the Weeting brothers tell him they are off to join the military.

The Herriots prepare to move to Rowangarth and another emergency with Granville Bennett.

James meets a pair of elderly twins. Oliver and Roland Strong, rabbit breeder and prize cabbage-grower respectively, have divided the cottage left to them by their mother and have not spoken to each other for 50 years. Now Oliver is convinced that Roland has poisoned one of his rabbits.

Siegfried is perplexed when the usually-caring Grandma Clarke snubs her neighbor, Franco Pedretti, who is the new shepherd on the estate where she is a tenant farmer. It soon becomes apparent that she blames Franco for the untimely death of her son in Italy during the war and the subsequent death of his wife in childbirth.

Sigfried declares that the business is in shambles financially, and his solution is Miss Harbottle, a meticulous secretary who rules the cash box with an iron hand. Amid a relentless succession of new faces - many gruff, some eccentric - James meets the lovely Helen Alderson.

Tristan and Siegfried meet Roddy, a hobo and his dog who are passing through the area. Mrs. Hall needs to visit sick relatives for a few days and Tristan is assigned chief cook and bottle washer. He also has to do the spring cleaning, cook the meals and put in his time in the surgery. Siegfried is less than sympathetic when Tristan complains. Granville Bennett stops in wanting the vets to care for his dog, Phoebe, who needs an minor operation. He invites James and Siegfried to lunch the next day and James once again over imbibes. Helen practices her first aid skills on James.

James and Helen are about to celebrate their first wedding anniversary and Tristan suggests to James that they go to the Harlequin, a modest restaurant that opened recently. It turns out to be anything but and is in fact one of the poshest restaurants in the area. Siegfried starts seeing Margery Egerton. Tristan, now a free man since being forbidden to see Miss Mount, sets his sights on previous conquests. Siegfried and Tristan ask James to arbitrate when they both want the same evening off. James has to pay several visits to Mr. Bailes whose dog seems to take great delight in scaring the wits out of him.

James musters the courage to visit Helen after she's seen him at his worst. Siegfried resorts to sorcery to aid a gypsy's ailing pony, and a wild ghost chase solves the mystery of the shrouded figure haunting Raine Abbey.

The sport of kings beckons James and Siegfried to the Broughton Races — James in search of a dead cert to raise forty pounds for a Mediterranean honeymoon, and Siegfried in pursuit of a dream job at the track.

As James struggles to save the dairy herd in which a friend has sunk all his savings, he discovers a colleague's guilty secret.

Christmas at Skeldale House can be a formidable undertaking, what with sick foals, overfed dogs and a skeleton guarding Siegfried's secret hoard of goodies.

Mr. Biggins tells James about his cowhand, Ned Finch, who goes drinking every night and is drawn to the bright lights of the big city. All James ever sees is an amiable fellow having a quiet drink in his local pub. Mrs. Hall is all aflutter with the visit of Mr. Barge, the loquacious pharmaceutical representative. Mrs.Pumphrey is worried when her new boxer, Cedric, proves to be overly flatulent. James finds a perfect solution. Mr. Beresford's dog is still misbehaving in the car. Siegfried suggest a new sedative, but it unfortunately doesn't have the desired impact.

Siegfried has become a bit horse shy given his recent experience with Dolly. James has to deal with the very unpleasant Ralph Beamish, an arrogant horse owner who continually ignores his advice. Siegfried visits a local pig farmer and fears his animals may be infected with foot and mouth disease. Mrs. Beck continues to complain about her with the vets bill and is now worried about how her cat might survive a gas attack should war be declared. Germany has invaded Poland and the British government has given Germany an ultimatum to leave or they will be at war.

The Darrowby Bell Ringing Society is suspending its operations for the duration of the war and they have one, final "meeting" at the local pub. James and Tristan go to the bell tower with not unexpected results. The vets have to deal with a series of dog poisonings. They soon identify the farmer responsible, but not before several more animals die. Siegfried treats Joan Clifford's dog Saxon, but the case has very specific implications for her. James treats Mr. Hanson's pigs but it's Mr. Hanson who is most entertaining in that he always speaks at the top of his lungs.

James treats Paul Cotterell's dog Theo, who has been losing weight and is diagnosed with Hodgkin's disease. James recommends that Theo be put down and Paul agrees. James doesn't realize the impact this has on Paul and the tragic results that ensue. James meets Lord Hulton, a hard working farm owner despite his aristocratic background. Hulton takes a liking to a horse that has wandered onto his property from the nearby military depot. At the Billings farm, James finds young calves who are wasting away. He thinks they have ingested an irritant of some kind, but the vets simply can't isolate it.

Siegfried takes Tristan to task for not mending a hole in the fence. Tristan announces that he now refuses to subject himself to Siegfried's tyranny but he is given 24 hours to mend the fence or face the consequences. Tristan tries to recruit James in his battle with Siegfried, but James will have nothing to do with it. Siegfried comes up with the perfect response. James operates on a sick calf but those assisting him are worse off than the calf. As a result, James comes down with a bad case of the flu. James is also concerned at having to give bad news to Andrew Vine about his dog, given his recent experience with Paul Cotterell.

Deidre and Calum are busy planning their wedding. Deidre discusses her future with Helen, who hopes the couple will stay in Darrowby. However, Calum gets offered a job in Nova Scotia. Siegfried, believing he has forced Calum into applying for the job, hopes he can now persuade him to reconsider.

When James treats a sick cat, he finds himself in an awkward position with Mrs. Pumphrey and Mrs.Tibbett. These two formidable and mutually ferocious Darrowby matrons compete both in presents for the invalid and in hounding James for information of the patient's progress.

Jenny Garston and David Rayner, individually charming farmer and horse-breeder, have been sworn enemies since their earliest school days. When a triple birthday is marred by tragedy it falls to Siegfried to negotiate with the stony-faced neighbors.