Charlie's father commits suicide and he has a hard time dealing with it. He discovers that his mom was having an affair with his dad's best friend and gets super angry at her about it on top of grieving over his father. He strikes up a friendship/something more with Maggie (Emmanuelle Béart), a French dominatrix trying to get custody of her son back. Maggie is struggling because her social worker is blackmailing her into having sex with him.
Eventually Charlie (Harrison Gilbertson) and Maggie make love/acknowledge their feelings. Maggie confronts the social worker and Charlie makes peace with his mom. After they part ways, Charlie goes back to being a normal teen, running on a track team, and when they're running through a park, he stops to take a breath and sees Maggie playing with her son. Then he rejoins his team without speaking to Maggie and the films ends.
A Little Longer:
Charlie's father commits suicide and he has a hard time dealing with it. He discovers that his mother was having an affair with his father's best friend and lashes out at her. Both of them struggle to communicate with each other and Charlie is extremely angry with her for it.
Meanwhile, Maggie -- a French dominatrix -- is being blackmailed by the social worker in charge of her son in foster care (who she lost custody of because of some issues she had with drugs). Charlie becomes fascinated with her and works his way into her life -- first by sneaking to see what's happening in her house, then taking on her gardener job. They strike up a friendship/Charlie's got a crush on her. He fantasizes about her and then convinces her to dominate him on a few occasions. He also takes her on a date (he's sixteen so it's to an arcade) and decides he's in love with her. The social worker blackmailing Maggie into sex gets jealous of Charlie and threatens him. Also, Charlie's Mom see some of the lash marks and gets worried/confronts Maggie and demands she fire Charlie.
Charlie goes to Maggie's house after she fires him. He throws her patio furniture into the pool and then, after calming down, she comes out to him and invites him inside. She gives him a cup of tea and says it's the last cup of tea they'll have, then he'll come over to the couch, they'll kiss and make love, express all the feelings he says he has for her and then they'll go their separate ways and he'll never, ever come back to the house again. He says, "Yes, mistress," but she says it's between them, no more mistress.
They start kissing and he takes her clothes off, then next we see the social worker arrive -- he looks at the patio furniture in the pool and then goes into the house. He asks about it from the doorway only able to see Maggie sitting on the couch. She calls him over and Charlie sits up so that the social worker sees him. Maggie tells the social worker it's over -- he tries to grab her and Charlie jumps on his back -- Maggie gets the whip, whips close to both of them, and yells for them to leave.
Charlie goes home and his mom has invited a social worker/counselor type person, Alice, to ask Charlie about Maggie. Charlie lays face down on the couch and refuses the answer the woman's questions and storms off. Then his mom tries to kick Charlie out -- telling him that she can't live with someone who hates her so much anymore. Later on, as Charlie is sitting in his dad's chair, the two finally share their grief and hug and cry.
Charlie goes to Maggie's house one last time and finds it mostly empty. Her room full of whips, etc. has been disassembled. Charlie goes to her son's room and sleeps on the bed. Maggie comes in in the morning. They say hello and he asks if she's all right. She assures him she's fine and she says she's back to pack up the last of her things.
She says, "Whoever gets you is going to be lucky."
Charlie says, "I think we should say goodbye."
He says, "I'll call you. Don't answer."
She says, "I'll beg you to call me. Don't."
He says, "I'll walk past you on the street. Ignore me."
She says, "I'll tell someone that I love them. It won't be you."
He kisses his hand, puts the kiss in her hand, and folds her hand up around it, thanks her and then leaves. Next we see Charlie looking at his father's suit as his mother is doing needlepoint. She tells him that it was his dad's favorite and he says he'd like to keep it for when he gets older.
Last we see Charlie running with a bunch of kids in uniforms, like on a track team. He stops, a bit out of breath, and looks over at the playground. He sees Maggie in a dress, playing with her son, smiles, and then runs to catch up with his team.