It's a bad morning at the mercantile. Harriet Oleson is acting like a battle axe (what's new), Nellie is demanding that her father drop everything to help her at the restaurant, and Willie is, well, being Willie. After exclaiming aloud, "Lord, deliver me from my family!", Nels decides to quickly put together a mobile mercantile and hit the road.
While traveling, he comes upon a boarding house, run by the fetching Molly Riordan, a happy, singing, single and beautiful Irish woman. And unlike Harriet Oleson, she can cook. The attraction on both sides of the equation is immediate, and trouble begins when Nels tells Molly that he's unmarried. Nels becomes a regular at the boarding house, considering it "home base" while he's on the road, returning to Walnut Grove just long enough to re-stock his wagon. A G-rated romance blooms, but on the day that Nels finally decides to give Molly a PG-13 rated kiss, who should walk into the boarding house but Charles Ingalls. Both men are flustered; Charles suddenly decides he doesn't need a room after all and Nels beats a hasty retreat to his room. Upon returning to Walnut Grove, Nels talks to Charles about how "confused" he is, asks him to keep the matter private, and tells Charles that he "hopes he understands". Believe me, Nels, we know Harriet, and we ALL understand.
In the end, the always-do-what's-right Nels Oleson confesses to Molly that he's already married and returns home, where a grateful and temporarily docile Harriet welcomes him with open arms. The final scene has them laughing together in the cool night air.
I love this episode and find it to be very realistically presented. In today's world, though, Nels would be gone in a heartbeat, sending monthly support checks back to Walnut Grove.