My wife's parents invited the four of us on a family trip to a hot spring resort. My father-in-law had ordered me to abstain for a month while my wife and I tried to conceive, and I was determined to finally fuck her that night. Then an unexpected argument erupted between us. With a month's worth of pent-up lust and nowhere to put it, I could only stare helplessly at my rock-hard cock. Unable to sleep that night, I headed to the baths to clear my mind—only to catch an intoxicating glimpse of my mother-in-law bathing...