The young heiress Ellie Andrews (Claudette Colbert) narrowly escapes from her overbearing father, jumping off a cruise ship and swimming to shore. She's upset because her dad won't let her live with King Wesley, even though she has already married him… against her father's wishes.
On land, Ellie meets newspaper reporter Peter Warne (Clark Gable) while riding the night bus northward from Miami to New York. She keeps her identity secret because her father is already searching for her. Warne is onto her but says that he'll keep Ellie's identity secret, since her whole socialite set is just "a lot of hooey" to him. Ellie offers Peter money to keep quiet, but he refuses, saying he'll help just because.
Antics ensue as Peter and Ellie get involved in mishap after mishap. Ellie's bag is stolen, leaving her with only $4 for the whole voyage. She then misses the bus—luckily, Peter waits for her.
Well, the next bus our pair of travelers board has to stop because of a bridge closed due to flooding. This forces Ellie and Peter to spend a night together, since space in the nearby "auto camp," or campground with cabins, is limited. Peter pretends to be Ellie's husband to prevent her from being recognized. This offends her at first, but she makes peace with the arrangement after Peter puts up a barrier to separate their two twin beds: In the middle of the room, he hangs a blanket that he calls "the Walls of Jericho."
The next morning, detectives sent by Ellie's father to search for her arrive at the campground. To evade them, Peter and Ellie put on a show, pretending to be loudly squabbling spouses. Their performance is convincing enough to send the detectives away, but it's also great fun for Peter and Ellie, who discover that they both love hamming it up. Meanwhile, Ellie's worried father continues to search high and low for her.
Back on the bus, a sing-along's in progress, and everyone gets along swimmingly until the distracted bus driver swerves and crashes. No one's hurt, but everyone's shaken up, including a mother and son who are faint with hunger: They've spent all their money on bus tickets and can't afford to buy food. Ellie gives them the last bit of money she has left.
Peter has to pretend to be a tough guy to scare away a fellow bus-rider, Shapeley, who's onto Ellie and who threatens to reveal her identity. Peter deals with this threat and sends Shapeley away. But Shapeley's threats—and the possibility that Ellie might be found out if the scaredy cat spills the beans when he gets to where he's going—force the two partners-in-secrecy, Ellie and Peter, to break away from the broken-down bus and its passengers.
Peter and Ellie are on foot now, making a quick off-road getaway and even crossing a river until they stop for the night on haystacks near a farm. (Still no rolls in the hay for these two, though—at least not yet.) Ellie complains about being both afraid and hungry and tells Peter that he's getting grouchy. She also says he can leave whenever he wants. Nevertheless, when he leaves to fetch food, and she mistakenly thinks he's left for good, she panics. We sense that she's falling in love, and Peter seems to be softening up, too.
Still, Peter delivers a lecture about all that's wrong with Ellie and people like her: rich people who don't know what they want, or what's really important in life. Ellie takes this in without responding.
The next day, the two runaways are still hungry, and they're hitchhiking. Peter mansplains how to hitchhike, but Ellie turns out to be much better at waving down passing cars. Unfortunately, the first stranger to give them a lift turns out to be a dud—more specifically, a "road thief." He drives away with their suitcases and only gives them up after an off-screen fight with Peter.
Meanwhile, Ellie's father makes a deal with King Westley, the man Ellie has already married. Instead of standing in the way of the marriage, Andrews will get out of the way, since this should make Ellie come home. Andrews publicizes this decision in the papers and even has King Westley give a press conference to announce that he and Andrews have reached an agreement.
In the next scene, Ellie reads all about this agreement in the newspaper. Although she and Peter are finally approaching New York, they spend one more night away together. Peter tricks the keeper of another campground into thinking that he and Ellie are going to stay a week so that they won't have to pay for the room, which they're planning to leave the next morning. While Peter puts up "the Walls of Jericho" again, Ellie asks whether she'll see him back in New York. He says no, because he doesn't "make it a policy to run around with married women."
This devastates Ellie, who tearfully declares her love for Peter. But when he asks if she means what she's just said, she's already asleep. He decides to take matters into his own hands and sneak away to New York. Here he tells Gordon, his boss at the newspaper, that he has exclusive access to a story: One about how Ellie Andrews isn't really going to marry King Westley. When Gordon asks whom she's going to marry, Peter says she's going to marry him. He also asks Gordon to lend him $1,000 "to tear down the Walls of Jericho," and he says that he's in love with Ellie.
Back at the campground, the owner and his nagging wife discover that Peter has fled with the suitcase (which we've seen him sell for gas money), leaving Ellie all alone. Since Ellie has no money to cover the cost of the room, the owners kick her to the curb—literally. They won't even let her use their phone to call New York.
Gordon lends Peter the money he asked for and looks forward to publishing the sensational story of Ellie's new marriage. But just after the editor has ordered the folks in his office to stop the presses, he gets a call from someone who tells him that Ellie has contacted her father, who's ordered the police to escort her back to New York so that she can be married to King Westley after all.
On his way back to the campground, Peter sees Ellie with the police escort and realizes that he has just missed her. Dejected, he returns to the office to give Gordon's money back. All the newspapers are already announcing Ellie's upcoming marriage to Westley.
But at the Andrewses', Ellie's father can tell that she's not looking forward to the wedding at all. She comes clean, admitting that she's in love with a man named Peter Warne, who thinks she's a spoiled brat and who judges Ellie's father, too, for the way he raised her. Andrews recognizes Peter's name because he has just received a letter from him requesting a meeting "about a financial matter in connection with Ellie."
Both Ellie and her father assume that this means Peter only cares about the $10,000 reward that Andrews was offering in exchange for Ellie's safe return. In fact, though, when Peter appears in Andrews's office, he only asks for $39.60. This shows that he doesn't care about money. He shows no interest whatsoever in the reward, and when Ellie's father finally asks straight-up whether he's in love with Ellie, Peter admits that he is.
Ellie eventually summons the courage to leave King Westley at the altar. This is all the more embarrassing for the showy aviator since he has made his arrival at the wedding into a spectacle, flying in and landing an autogyro to wow the guests. Too bad for him, he's lost the game.
In the end, we don't see Ellie and Peter, but we know they're on their honeymoon. We hear the campground's owners talking, and it's clear from their references to blankets and an annulment that, as in the Bible, the "Walls of Jericho" are finally coming down.