Miles, an English teacher, takes his soon-to-be-married best friend on a weeklong trip to California's wine country. The two have different ideas in mind as Miles is interested in wine tasting, while Jack is interested in a having one or two flings before tying the knot with his fiancé.
If they want to drink Merlot, we're drinking Merlot.
No, if anyone orders Merlot, I'm leaving. I am NOT drinking any fucking Merlot!
Sideways starts with Miles sleeping in, and showing up at Jack's house later than they had planned. It's becomes obvious that Jack can't wait to get out of there, and so they begin their trip to wine country. While driving up there, we learn that it's Miles' mother's birthday. Miles tells Jack that it'll only be for a short while, but they end up eating dinner and staying the night. They finally leave the next morning without waking Mile's mother.
After arriving at their destination, Miles and Jack go out to dinner at The Hitching Post. We see Maya working there as a waitress. They talk to Maya after her shift, and she sounds interested in doing something, but Miles tells her that they're tired from the drive. Jack expresses his disappointment on the way back to the hotel.
While out wine tasting, Miles and Jack run into Stephanie. Jack asks Stephanie if she knows Maya (she does), and so plans are made for the four of them to go out for dinner. After dinner, they go back to Stephanie's house. Jack and Stephanie hit it off right away, while Miles puts up an emotional shell towards Maya. It's obvious that he likes her, but the pains of his former marriage are preventing him from getting close to someone. He eventually forces himself to make a move on Maya, but the mood has passed, and she declines. Miles leaves that night in disappointment, but with a glimmer of happiness -- Maya is interested in reading Miles' unpublished novel.
The four of them continue to hang out during the course of the week, and Miles and Maya eventually sleep together. It appears to be a budding relationship, but it is soon ruined when Miles lets it slip that Jack is engaged to be married. After the startling discovery, neither Stephanie or Maya want anything to do with Jack or Miles. The entire trip has turned out to be a disaster.
While Jack and Miles are eating dinner, a waitress recognizes Jack from an old TV show, and he goes back to her house for the night. Jack shows up naked back at the hotel room, explaining that the waitress' husband had come home while they were having sex. Miles finds it hysterical, but Jack frantically tells Miles that they have to go back for his wallet because their wedding bands. They go back to the house, and Miles is the one to sneak in and grab the wallet. He's chased out of the house by the waitress' naked, screaming husband. They eventually make it home alright, and Jack's wedding happens as planned.
Sometime after the trip, Miles checks his answer machine to find that Maya has left a message. She invites him back to her place the next time he ends up in wine country, and the movie ends with Miles knocking on Maya's door.