The movie opens in 1969 as Frances McDormand is lecturing her daughter about sex, drugs and rock and roll. Her daughter, now 18, can't take it anymore and leaves home to become a stewardess. She leaves 11 year old William (who has always thought he was 13) her record collection.
This collection changes his life. Four years pass and he has now learned everything about the artists and the music. In fact, he writes a music column in his school paper. He contacts the editor of "Cream" magazine and gets lessons and encouragement about his writing. This editor likes him and gets him passes to the Black Sabbath concert to write a small review of the concert.
While trying to get backstage before the show, the security guard won't give him the time of day. Hey, he's "not on the list". William meets a few groupies who are also trying to get in. No luck. Finally, the opening act, STILLWATER arrives. William notices an opportunity and starts shouting out compliments to the group. The lead guitarist of the band, Russell, stops and listens to William carry on about their songs. Russell lets him in along with the other groupies.
The leader of the groupies is Penny Lane played by Kate Hudson. She doesn't consider herself a groupie thinking instead that she inspires the band. She refers to her and her friends as Band-Aids. William is instantly attracted to Penny as she is very charming and worldly. She ask William to someday go to Morocco with her. Russell gives William a quick interview and is impressed with him. He invites William to their next concert. William goes to the next concert in LA and finds Penny there also. Turns out that Penny follows Russell from town to town and is more than just a groupie, she is in love with Russell. Russell isn't in love with her, although he is very attracted and has deep feelings towards her and even though he's married, sleeps with Penny when he's on the road.
Somehow, ROLLING STONE magazine reads William's articles and is very impressed. They would like William to write an article for them and will pay him $1000. William asks if he can cover STILLWATER and they agree. He will go on the road with the band covering everything that happens. The band isn't sure about it since he is the "enemy" and will destroy them. Russell defends William and says he can be trusted.
Once he's on the road, riding the bus with them, he sees another side of the band. The main problem is the ego struggle between Russell and the lead singer, Penny and the rest of the groupies are there and William can't stand the thought of Russell and Penny together. Slowly Russell gives William a little information for his story. It turns out that Russell wants to quit the band but as they get more and more famous, he can't let his other band members down.
As the tour gets closer to New York, Russell realizes that he must get rid of Penny since his wife will be in New York waiting for him. During a poker game, he sells his groupies to "Humble Pie" for $50 and a case of beer.
Penny goes to New York anyway on her own and during a dinner with the band and their girlfriends and wives, Penny shows up in the background. The band manager asks her to leave and she is devastated. William goes to Penny's room and finds her overdosed and on the verge of death. While trying to wake her up, he tells her he loves her. The doctors come and pump her stomach.
On a plane ride to another concert, the plane is in trouble and looks like it will have to make a crash landing. Everyone including Russell's wife is panicking and shouting at each other. The lead singer tells Russell he has slept with his wife. Russell shouts back at him but the singer says who cares, you're sleeping with Penny. Just as it's about to crash, one of the band members shouts out that he's gay. Suddenly the plane recovers and all is well and quiet again. Everyone looks at the now "out" band member as he shrinks down into his seat. (Pretty funny scene)
ROLLING STONE calls and wants the story. As William is leaving to fly to San Francisco, Russell tells him to go ahead and write whatever he wants. The Rolling Stone editor loves the story and can't wait to publish it. First they have to ask the band to verify it. They don't, saying it is all lies. ROLLING STONE won't publish it and are pissed at William for fabricating the story. William is crushed. While sitting dejected in the airport he sees his sister the stewardess. They go back home together.
Back on the STILLWATER tour, one of the groupies tells Russell how horrible he was to Penny and to William. Russell calls Penny and wants to meet with her. He asks for her address. Penny, feeling bad for William, gives Russell William's address instead. Russell goes to the house thinking it's Penny's but Frances McDormand answers and lets him talk to William. The two of them talk things through.
The final scenes are a picture of the cover of the ROLLING STONE with Russell's picture on the front with the rest of the band behind him.
We then see Penny buying a ticket for Morocco.