James hasn’t been in Yorkshire long and he already has competition, both professional and romantic. Siegfried’s younger brother Tristan is returning home from veterinary school. Siegfried sends James to pick him up from the train station—in the nice car, to spur Tristan to “apply himself as Herriot has done.”
That may be asking too much. Tristan stole his ride on the train, hiding in the mail car in his tuxedo. He grabs the car keys from a surprised James upon meeting him and hops in the driver’s seat. He’s as reckless a driver as his older brother, and swerves off the road after nearly hitting another car. The bumper on Siegfried’s car is damaged, but Tristan ties it back on. Siegfried will never notice.
Tristan excitedly tells his brother that he passed his last exam. Siegfried is overjoyed that Tristan has finally finished school—although Tristan does have to stay in the cupboard, since James now lives in his old room.
Tristan doesn’t believe James will last long, however—he keeps making comments about all of Siegfried’s abortive assistants—and is eager to prove himself. He wakes up early to organize the pharmacy, then steals a sausage from the later-rising James’s breakfast plate.
Siegfried sends Tristan along with “Jim,” as Tristan calls James, on rounds, despite Tristan’s reluctance. James has to return to a farmer whose cow won’t stand up. The farmer has already shown skepticism about James, whose initial diagnosis has been proven wrong. While James tries a different dose of medicine, Tristan eats and gabs with the farmers. After the farmer suggests yelling at the cow and Tristan says he’s willing to try it, James insists that he’ll do it. Tristan then laughs at the spectacle.
At their next stop, however, James proves more popular than Tristan. The wealthy Mrs. Pumphrey’s pampered dog Tricki Woo has a problem that James quickly fixes. Tristan once stood on Tricki Woo’s tail, so he’s already in bad standing. But James also delights Mrs. Pumphrey and garners an invitation to a party she is throwing. Tristan is not invited.
Next, James and Tristan stop by the Alderson farm. Tristan silently notes James’s interest in Helen with a smirk.
Back at Siegfried’s, Tristan and James fight over who should feed the animals—both want to prove themselves to Siegfried. James tries to rush out to visit the farmer with the ailing cow without anyone noticing, but Siegfried orders Tristan—this time he’s the late riser—to join James.
At the farm, James declares the cow’s pelvis is broken, and urges the farmer to send the cow to the butcher. Nothing can be done.
Meanwhile, Siegfried wants to reward Tristan—he’s excited to have two qualified assistants, and proud of his brother. Happening upon Mrs. Hall as she meets an old friend, Dorothy, for tea, Siegfried compliments Dorothy's car. She wants to sell it, and he decides to buy it for Tristan. She has one condition: look out for Mrs. Hall. Her son has broken her heart several times already, and she continues to send him money, “no matter what he’s done.”
Having family members who continually disappoint them gives Siegfried and Mrs. Hall something to commiserate about, but when Mrs. Hall tries to ask Siegfried about his love life, he draws a line.
After Siegfried excitedly presents the car to a shocked Tristan, he and James set off for Mrs. Pumphrey’s, James in a tuxedo borrowed from Tristan. “Uncle Herriot,” as Mrs. Pumphrey calls him, is set to watch over Tricki Woo, while Siegfried goes off to dance and enjoy the party.
James at least gets some human company when Helen comes over to speak with him. She mentions how Siegfried will dance with plenty of women, but never the same one twice. James finally works up the courage to ask her out—but then her date, a man named Hugh, appears and gives her a kiss. They leave James to go dance.
He doesn’t have much time to digest this disappointment, as Siegfried pulls him aside and tersely demands that they go for a drive.
Siegfried has learned that James recommended a cow to be butchered—and that the cow has recovered. Arriving at the farm, James is surprised to find the cow on its feet. Siegfried angrily realizes that James misdiagnosed the cow, which had recently calved.
Luckily for James, Tristan has his own disappointing news to redirect Siegfried’s anger. Mrs. Hall has learned that, while Tristan did pass his final exam, he didn’t pass two others. She reassures him that Siegfried will never stop caring for him, but that he must tell Siegfried the truth.
When Siegfried and James return home, Mrs. Hall suggests that James and she retire, leaving Tristan to tell Siegfried about his exams. After surviving an outburst from Siegfried, Tristan joins Mrs. Hall and James, and he and James bond over making Siegfried angry. The only way we’ll survive Siegfried’s eccentricities is if we stick together, Tristan tells James, who agrees.
Siegfried puts the new car up for sale, rescinding Tristan’s gift. He also finally notices the broken bumper on his own car, and screams for Tristan and James. They scurry off and hide, laughing.