Kari and I had always been a pain in the ass to each other and after our folks died in a car wreck things just got worse. I was nineteen when she got married to Don and kicked me off of the estate and I ended up in a shitty little apartment in the bad part of town. I managed for a year and then the company I worked for went into Chapter 7 and that was that. The only upside was the company lawyer told me a legal right to live back at home so I enlisted his aid and was soon back at home in my old room. I immediately decided to make life miserable for Kari and the best way for me to do that was to be a tease to Don. I'd go around the house in one of his shirts and just a pair of panties, after making sure the air conditioning was on first. She'd leave for work in the mornings and I'd make him breakfast while all I wore was a silk peignoir that showed off most of my 34C's. At night when I knew he was up late working on a project I'd go skinny- dip in the pool, knowing he'd see me out the window. My mistake was that I never once thought about how Don felt, all I could think about was getting at Kari by getting him all hot and bothered. I didn't have a lot of experience with men and I had no idea what I was messing with. After six straight months of this I guess I didn't plan on my comeuppance...so to speak. My ovulation cramps had been pretty bad this one night and I woke up needing some serious relief. I padded out to the bathroom and popped three of Kari's Midol and then decided to hit the hot tub to ease the aches a bit more. I went out the back door to the pool and the hot tub and got the extra bonus of seeing the light on in Don's study. I was going to go naked anyways, but I made an extra show of it as I stepped out of my panties and then unbuttoned one of Don's shirts that I'd appropriated for a nightshirt. Naked, I slipped into the soothing heat and felt the cramps begin to abate. The relief was amazing and I decided to use the built-in lounge in the hot tub to relax even more. I stretched out my legs to the pedestal in middle of the tub and felt the world start to slip away. Sleep hit me like a truck and I remembered as I was dozing off thinking about how it was just like being in my mother's arms again. When I woke up the water was sloshing a little bit and the pool lights were all off. It was a little disorienting to be in the dark like that, but I didn't panic. Actually, I figured it was safe since there wasn't anyone around for a mile or so and I just put my head back and drifted off again. I woke up again to the feeling of someone pulling me out of the lounge. "Wha-wh-wah's going on?" I said to the ink-black night. "It's okay, it's me." Don's familiar voice settled me down, but I still felt a tinge of panic at how dopey I felt. "You did know," he went on, "that Kari keeps her Vicodin in her old Midol bottle since it's easier to open. I heard you open the bottle and was a little concerned you'd drown out here." I rested my head on his shoulder since it seemed so heavy to hold it up on my own. "Thanks, Don, you're the best." Then the thought hit me that Don's shoulder was holding my head up. The confusion of reconciling my former reclining position with wherever I was now made me fidget a bit to feel around myself. "Shhhh, baby, you're with Don and you're just fine." I calmed down a little and brought my ankles in to my belly and found something blocking them. I rubbed the heels of my feet around and felt them touching skin... but not my skin. It was Don's back. "Yeah, that's right baby...wrap your pretty little legs around me... mmmmm." He pulled me tighter and I felt the warm water gush up between my breasts as our bodies met. "Don... wha... what are you doing?" I found the strength to pull my head up to face him, except that I couldn't see him in the dark. "Sweetie, I'm gonna show you what you've been messing with since you moved here." He pulled me tighter and his lips sought out my own and he began the softest, most passionate kiss I'd ever had in my life. His hands roamed freely over my naked body and I felt myself responding to his kiss with a kiss of my own. The drugs made me feel as if I was watching this all take place from somewhere else. We were in the middle of a kiss when he cupped my ass with his hands and gently lifted me in the weightlessness of the water. His cock slipped up between my pussy lips and then came to rest between my ass cheeks as he lowered me. "Don, we can't... I can't... I'm not protected... you're Kari's..." He didn't try anything right off and just resumed kissing me. I lost track of time as we kissed and then he began the most exquisite grinding of his cock between my pussy lips and I felt my senses whirl. The grinding became more strategic as he pulled me tighter to grind his cock into my clit. I was beginning to feel the onset of a wonderful, warm climax when he lifted me up again and I felt his cock pry at the door of my pussy. "Don," I protested, "I can't... you know." He thrust into me, just enough. "I swear I won't come in you... I promise." What the fuck was I thinking? I kissed him and ground into him. "Okay... just don't come in me." That wonderful cock of his magically slipped into me and I was fucking my sister's husband. My whole universe quickly became that cock, sliding in... sliding out... fitting in to me... withdrawing... snuggling up to my cervix... pulling back. My delayed release began to build up and Don felt it, too. He held me tighter and drove deeper into me, making me gasp with the sensation of being penetrated so deeply. It didn't take long before I felt it start up. I don't know why, but some vestige of common sense told me to stop and I tried to lift myself off of that wonderful rod in my body. Don squeezed me tighter and drew me down, impaling me deeply on his beautiful tool. I felt it begin in my toes and sweep up my legs until it centered in my belly. My body fully opened to this available male, all I could think of now was the delirium cresting across my being. Don was building up to something himself and I felt his need building as my own peak drove me into a mating fury, humping at the cock in my pussy, making it hit my pleasure harder... deeper. Deeper... deeper into my body... inviting the male into my depths... to release himself. The thought cleared my mind even in the middle of the finest orgasm of my life! "Don, you promised... Please! Uunghhh!!!" He was the master. He drove his cock hard into me and brought me to this place I'd never even imagined. I was senseless and aware of everything all at the same time. I abandoned myself to my demanding need and answered his deep thrusts by spreading my thighs to allow him fully into my eager body. I was terrified when I felt his cock swell up inside of me and kiss up to my cervix. I knew what was coming. I couldn't help myself as I spread my legs even further. With a series of deep, quick thrusts, he buried himself to the hilt in my pussy, ramming his cock almost into my womb, and then let loose his jets of sperm-laden come into my fertile belly. I never thought he'd stop coming. It just seemed to go on forever as my life changed irrevocably. He relaxed and held me tight with his throbbing cock still twitching sperm into me. I began to cry a little and he kissed me gently. "Shhh." He rocked me in his arms for what seemed like hours. Then I felt him push into me again. In the darkness he didn't see me crying as his swelling cock began to thrust itself into me again. I just sat there as he mated himself to me again and soon I felt him spurting his cream into my body for a second time that night. Not long after that the Vicodin claimed me and I can't remember what happened or how I got back to my room. The next morning I awoke to a sunny day and as I remembered the night's affair I wondered if it was just a dream. Kari opened the door to look at me. She seemed both pissed and somehow satisfied, as if in an "I-told-you-so" kind of way. "Didja like fucking my husband?" Her voice was saccharin sweet. Shit, I thought, I'm really gonna get it. And I was both right and wrong with that thought. "You better get used to it if you're gonna stay here and tease him." She turned as Don came up behind her and kissed her full on the lips. She looked him in the eye. "Be down soon for breakfast." He said to her as she stood there hugging him. Don kissed her again and I watched in disbelief as she turned and walked out the door. My disbelief was magnified when I watched as Don closed the door and his terry robe fell to the floor. There was already a glisten of moisture on his hard cock as he pulled back my blankets to reveal my naked body. I was speechless as he climbed onto the bed and knelt between my legs. I closed my eyes and felt him pull my thighs onto his and then his cock prodded between my pussy lips again. "Just lay back and enjoy sis, cause I'm gonna fuck a baby into you if it's the last thing I do." I was just about to beg him to stop when he slipped that magnificent cock of his all the way into me in one slow, electrifying plunge.