Speak begins with a central mystery: what happened to Melinda? She is ostracized from her high school community for calling the police to bust a party over the summer, and she feels like she can't tell anyone what's happened. Even when people insult and confront her about ruining the party, Melinda doesn't fight back or even acknowledge what really happened. She slips into a long period of silence, literally and metaphorically.
Only in the third marking period—much later in the novel—does Melinda relive that night at the party. It was her first high school party, and no one's parents knew where she and her friends really were. After drinking too much too quickly from nerves, she goes outside and encounters Andy Evans, a handsome senior boy who looks like a "Greek God." He recognizes that she's drunk as she leans against him, and he reaches down to grab her butt, then kisses her twice, hard. Because she's drunk, she doesn't quite realize what's happening, but then they're on the ground, and he rapes her; as she struggles and tries to scream, he covers her mouth. Once it's over, she calls the police for help, sealing her fate as a social outcast. Because everyone judges her and bullies her for calling the police, she doesn't feel like she can speak out about what happened to her.
From page 135 of Speak:
We were on the ground. When did that happen? "No." No I did not like this. I was on the ground and he was on top of me. My lips mumble something about leaving, about a friend who needs me, about my parents worrying. I can hear myself—I'm mumbling like a deranged drunk. His lips lock on mine and I can't say anything. I twist my head away. He is so heavy. There is a boulder on me. I open my mouth to breathe, to scream, and his hand covers it. In my head, my voice is as clear as a bell: 'NO I DON'T WANT TO!' But I can't spit it out. I'm trying to remember how we got on the ground and where the moon went and wham! shirt up, shorts down, and the ground smells wet and dark and NO!—I'm not really here, I'm definitely back at Rachel's, crimping my hair and gluing on fake nails, and he smells like beer and mean and he hurts me hurts me hurts me and gets up
and zips his jeans