Locked in their shared room, sister and brother find themselves alone, their parents out for the night. Boredom turns to curiosity, and they begin to explore each other's bodies. He tentatively touches her breasts, she wraps her hand around his hardening cock. They're both inexperienced, but their desires are clear. She guides him inside her, and they awkwardly, beautifully fuck for the first time, their moans filling the silent house, their bodies learning each other's rhythms.