On the Fourth of July, the Simpson family takes a road trip to visit a cabin in the woods. While driving there, they pick up hitchhikers Squeaky Voiced Teen and his girlfriend, Beatrice. Staring at the two younger teens, Homer flashes back to how he and Marge were, twenty years earlier in their dating years. In the flashback, a young Homer and Marge are on bikes, riding down the highway. Homer and Marge attempt to kiss while biking, but Homer ends up crashing his bike, forcing them to continue on foot. Ned and Maude Flanders, who are driving by, see them and pick them up. Ned and Maude shock Homer and Marge by revealing the two of them are married (as of 2:00 pm that day). They appear to be having some marital problems already and, seeing this, Homer proposes to 'not' marry Marge. Back in the present, Homer becomes quite annoyed with the Squeaky Voiced Teen's kissing Beatrice, which prompts him to go into another flashback, five years ago in Homer and Marge's married years.
In their married years in 2004, Homer and Marge are more stressed. Driving with Marge, Patty and Selma, and getting the usual flak from the latter two, Homer reaches his breaking point and kicks his sisters-in-law out of the car. Marge points out that Patty and Selma have the map and therefore the directions to their destination. After mistaking the fuel gauge for a compass reading "E" for East, the car runs out of gas, and Homer and Marge head to a nearby home to use their phone. The house owner, Alberto, is having a party, and he invites Homer and Marge inside. Marge becomes annoyed with Homer's behavior at the party, and becomes enraged after seeing him flirt with a beautiful woman named Sylvia. Following an argument about this with Homer, Marge accidentally falls into the pool. Homer starts a sushi fight, and Marge regrets marrying Homer. In the present, the family drops off the Squeaky-Voiced Teen and Beatrice at a cabin, while the Simpsons head off to their cabin.
Homer and Marge flash back to their dating years, where the Flanders' dropped them off at the very same cabins they are at today. Flanders manages to successfully convince Homer and Marge to sleep in separate rooms, while Ned and Maude have sex, much to their disappointment. In their married years, Marge leaves Alberto's party with him to run to the cabins. Similarly, Homer runs off with Sylvia to those very same cabins. Not wanting each other to discover their own near-affairs, Marge hides Alberto in a box and has Homer put it outside; Homer, not knowing Alberto is in there, puts Sylvia inside as well. Alberto and Sylvia fall in love while Homer and Marge rekindle their love. In the present, Homer and Marge meet Alberto and Sylvia, now married with a daughter named Ruthie and learn of each other's near-affairs. Marge becomes disgusted that the most important moment in their early years of marriage was based on lies and deceit; however, Homer points out that Marge was just as bad as he was at the time, and that she has no moral to scold him. Homer regrets marrying Marge and, trapped in a ball of their luggage which happened while unpacking, has Ruthie roll him away from Marge into the woods but he gets hit by a pedal car driven by Bart with Lisa and Maggie inside.
Back in their dating years, Ned tells Homer that if he were married to Marge, he could make all the love to her he wants. Taking a walk through the woods with Marge, Homer carves the message "Marge + Homer 4ever" into a tree. In the present, Homer sees this message on the same tree and decides there is still time to save his marriage. He attempts to peel the bark off the tree and show the message to Marge; Marge suddenly arrives to find Homer and accidentally knocks the tree, which had severely weakened roots, over a ravine. Homer clings onto the bark and refuses to let go, but Marge tells him that their love for each other is within themselves, not in the bark. Homer falls down the ravine toward the river below, still holding onto the bark and peeling it all off the tree, with Marge falling after. They stop falling when the line of bark stops, allowing them to be saved by Bart and Lisa in their pedal car, which Bart had accidentally driven into the river. As the episode ends, Bart allows Homer and Marge to have PG-13 smooching in the back seat.