Then a very important character appears in William's world, the infamous rock critic Lester Bangs (Phillip Seymour Hoffman), who can relate to William perfectly: Bangs' mother was a Jehovah's Witness and his father had died when he was young. In 1969, Bangs began writing freelance after reading an advertisement in "Rolling Stone" soliciting readers' reviews. His first piece was a negative review of the MC5's album Kick Out The Jams, which was published. Bangs was fired from Rolling Stone in 1973 by Jann Wenner over a negative review of Canned Heat. Bangs moved to Detroit to edit the legendary magazine Creem, which is shown in the movie read enthusiastically by William, so when both writers meet, the connection is instantly produced after chatting about Lou Reed's missteps (Lester's allegiance with the ex-leader of The Velvet Underground came from 1968 in San Diego) and Lester Bangs becomes William's mentor.

William is going to need Bangs' advice about rock and roll lifestyle and the dangers of "the industry of cool", because he's suddenly hired by Rolling Stone to cover a new group called Stillwater which is on the road looking for success and their band leaders, Russell Hammond (Billy Crudup) and Jeff Bebe (Jason Lee) want William to act as a promotional scribe for the group, although he's often mistrusted and defined as "the enemy" because William is really an objective witness of this modest rock band struggling and touring with a homely manager Dick Roswell (Noah Taylor), and only supported by their fanbase and the band-aids, three groupie girls who accompany them on tour, underaged women who use nicknames as Polexia Aphrodisia (Anna Paquin), Sapphire (Fairuzza Balk) and Estrella Starr (Bijou Phillips), friends with the queen bee of the band-aids, Penny Lane (Kate Hudson).

William cannot help developing a love interest towards the enigmatic Penny Lane, who refuses to tell him her real name and who has designed a glamorous unreal world inhabited by her fantasies and filled with booze, drug use, a bohemian vamp wardrobe and promiscuous sex with rock stars. Penny uses William's bond with Lester Bangs as the excuse to approach Stillwater's members and befriend them, esspecially Russell, the egocentric and talented front-man, whilst Polexia will be Jeff's girlfriend on the road; one night in the boring city Greenville William loses his virginity to all the groupies and the day after he feels so disoriented emotionally that he cries sitting in front of the locked up doors of the love nest that is the hotel room shared by Penny and Russell, unable to reconcile his mother's moral teachings with his recent experience in an amoral world of carefree sex.