(Unfortunately, I do not have the physical copy of this book and can't provide page numbers. I will add chapter titles to help.)
The inciting incident in Speak happens before the novel begins and is not revealed until about a quarter of the way in the book in the section "Devils Destroy" when a girl "pokes" Melinda in the back at a rally and asks "Aren't you the one who called the cops at Kyle Rodgers's party at the end of the summer?" Up until this point in the novel, Melinda seems like "outcast," as she refers to herself, because she is an awkward high school freshman who has been shunned by her closest friends.
However, this incident of calling the cops at Kyle Rodgers's party is just the first layer in a series of issues Melinda is dealing with. Laurie Halse Anderson slowly peels back these layers in order to create a sense of empathy for Melinda, who is struggling to deal with her high school experience. This party is what starts Melinda down her destructive path. In the chapter "Name, Name, Name," she says, "When I went to that party, I was abducted by aliens. They have created a fake Earth and fake high school to study me and my reactions."
In the chapter "A Night to Remember," Melinda recounts what happened at this party. She describes how Kyle, a junior-to-be-senior, lures Melinda, an eighth grader-to-be-freshman, into the woods behind his house. Blinded by the romantic promise of starting high school with an older boyfriend, Melinda follows him. She describes the rape scene in strong detail preferring denial to acceptance of what had just happened:
"I'm not really here, I'm definitely back at Rachel's, crimping my hair and gluing on fake nails, and he smells like bear and mean and he hurts me hurts me hurts me and gets up
and zips his jeans
Melinda reveals that this is what happens more than halfway through the novel, which is why it proves to be so effective in creating Anderson's desired effect: Melinda is not just a typical outcast freshman, but a survivor of rape who is afraid to tell anyone what happened. This crisis is resolved as Melinda learns about ways to cope with her rape, particularly her artwork. Eventually, Melinda finds her voice and speaks about being a victim of rape.