You're at your parents' house after a night out, surprised to find your prissy stepsister there, dressed up. When she stumbles in later while the parents are out, you pour a nightcap. You start dancing, hands on her hips, then kissing. She feigns resistance but melts. You undress her there. She asks about a condom—you don't have one. You see the risk excite her.
Then her husband calls. She bends over the sofa to answer, bare ass exposed. While she struggles to sound normal, you slide your raw cock in. She gasps, trying to stay composed, but her body gives in.
After the call, she's shocked but admits it felt too good to stop. You take her doggy, then missionary, whispering how wrong this is, how that makes it hotter. When close, she begs you to pull out, but you tempt her with breeding her, sending her back filled with your cum. She wavers but makes you withdraw. You cum over her stomach and pussy, lie on top resting in the mess, harden again and slide back inside for shallow thrusts, pushing your sperm deep before stopping.