When the Oleson's niece from Chicago, Kate Thorvald, arrives on the stage, she is hurt by a falling bag and taken to Doc Baker for treatment. Later, at the store, Kate asks her uncle about the doctor. She takes horse and goes riding. She rides over to the hill overlooking the Ingalls farm where Doc Baker is treating Jack for an ear infection. When the Ingalls invite him to supper, Kate sends her horse home and knocks on the door, saying she was thrown from her horse. She gets invited to supper, too. In bed, Mary tells Laura that she thinks Doc Baker is in love with Miss Thorvald.
After Doc Baker gives Kate a ride home she mentions that she has noticed his attention and asks him if he will go riding with her the next day. Mrs. Oleson comes out to express worry and overhears the offer and acceptance. The next day, Doc Baker and Kate go on a picnic. Afterwards, he drops her off at the house. Aunt Harriet asks her if Doc Baker is in love with her and she says she hopes so, making Harriet anxious. He is too old for her and too poor for Harriet. Kate tries to reassure her. She asks her if the preparations for the party Saturday night are complete and if she has invited Doc Baker. And she tells Harriet not to glare at him. Hanson expresses his disgust with Doc Baker's fling with Kate to Charles. That evening, during their weekly pinochle match, Hanson notices that the doctor is distracted and he discusses his attraction to Kate. The doctor is aware of his and Kate's age difference but he doesn't care. Kate decides to accompany the doctor on his rounds including a visit to the Ingalls dropping off some candy for the girls. Laura asks them if they are going to get married, amusing Kate and embarrassing Ma in the process. On the way home, Kate and Hiram kiss for the first time. As they rush to another call he asks her to marry him and she accepts.
Doc Baker goes to the Mercantile to buy a ring and Charles happens upon him. At the Oleson's party Saturday night, he gives her a ring he fashioned from one of his dad's watch chains. He promises to give her a better one when he can find it but she is taken with it. They kiss and Kate urges him to make the wedding announcement. He does and everyone except Mrs Oleson congratulates. In bed that night, Caroline and Charles discuss the impending wedding. Charles is OK with it until Caroline suppose what would happen if an older man wanted to marry one of his daughters--then he is not so OK with it.
At the mill, Kate and Hiram present their house plans to Hanson and he gets Charles to look at it too. Apparently the Ingalls have invited the new couple over on Saturday and Kate wants to know when to come. Charles suggests early so he and Hiram can go fishing. At the fishing hole on Saturday, Charles and Hiram discuss the impending wedding. When the finish, they head back to the farm where he spies Kate playing with Mary and Laura in the yard. When Laura asks the Doctor if he and Kate are going to have children and how her Pa is looking forward to grandchildren and great grandchildren, the Doctor realizes that he'll never be able to experience those things.
The next day, Kate visits Hiram and he talks about their age difference. Charles stops by to tell the doctor that Helga is in labor. Kate offers to be the midwife and they both head over to their farm. The doctor with Kate helps Helga through a difficult labor delivering her a daughter. When Helga asks him if she gave him as much trouble for her mama he realizes that he delivered both Helga and Ole and is now delivering their kids. Kate sees the writing on the wall.
Early the next morning, he drops her off at the Oleson's and he expresses his second thoughts about the marriage. He compares them to the seasons: she is in early Spring--he's in late fall--he's old enough to be her father. She tearfully agrees with him. She asks to keep the ring and kisses him goodbye. The next day, she boards the stage as Doc Baker looks down from his room.
"Doctor Baker didn't come by our house for a whole month. Pa said we shouldn't worry and he was right. In no time, Doctor Baker was on the road, making his rounds. Caring for the folks of Walnut Grove."





