My step-sister-in-law always flirted with me, but I never thought it would go further. One weekend, her parents left town, and I found myself alone with her. She invited me to join her in the bath, and I couldn't resist. We started kissing, and soon I was fucking her hard. The thrill of getting caught made it even hotter. We fucked until we were both exhausted, knowing we had to keep our dirty little secret.