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 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.

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.

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.

Mrs. Hall is away visiting a cousin and James agrees to fill in for Stewie Brannon while he's on holidays. Siegfried and Tristan make the best of it but Tristan's culinary skills have not improved over the years. He does make an excellent bangers and mash, for every meal, everyday. James treats a severely injured dog and has a bit of difficulty with the local dialect.

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.

James is busy with tuberculin testing but is summoned to the Ministry of Agriculture when the test results don't quite add up. Siegfried has to deal with a dog owner who only believes in strict discipline in dealing with his dog. He also has to deal with dying sheep, but the owners may not have the means to save them. Helen gets a job as a secretary, but James isn't quite sure he approves. Siegfried, on the other hand, thinks it's a wonderful idea. Tristan is less than enthused however when he realizes he will have to take over Helen's duties in the partnership. Mrs.Hall tells Siegfried that she has to leave to help her brother, who is now alone to work his farm.

The possibility of war is on everyone's mind with Helen preparing for the privations ahead and Tristan tasked to tape the windows in the event of bombing. Siegfried decides that they should conserve food and heating by eating their meals together, but Mrs. Hall takes his instructions to economize a bit too seriously. James treats Hamish, a sick dog who requires an operation and Tristan, who is tasked with overseeing his recovery, loses him. The vets forgo a posh evening out to treat a stray dog who has had an accident. Tristan is aghast at Siegfried's attempt to pair him with Deirdre Headingley, one of his crony's less-than-attractive daughters.

The vets visit a modern dairy farm and are left to wonder who benefits from the cold efficiency. Miss Westerman returns with her dog Hamish and Tristan tries to avoid her, given that he misplaced her dog the last time she him in the vets' care. She is concerned at the rumors that all dogs will need to be destroyed if war is declared but Tristan sets her mind to rest. The vets agree to spay a cat for a minimum fee, but find they may have gotten more that they bargained for. Siegfried treat Herbie Hinchcliffe's aging horse Dolly and becomes emotionally involved in the case when he has to put