She has a surprise for her husband, but she sleeps with her brother-in-law.
She has a surprise for her husband. She knows he loves surprises like this. But things don't go quite as planned, because the man who arrives at her house is her husband's best friend. She obviously doesn't know this, but she lets him touch and kiss her. Perhaps the scent is different and the kisses are even more tender and soft, but she feels so aroused that she ignores these small details and surrenders to the pleasure. Then she removes the blindfold and realizes the man in front of her, but her body can't stop and simply wants to feel deeper penetration.