My wife's sister saddled me on the train

We were traveling home on the overnight train after a week at the seaside. Four people in the compartment: me, my wife Marina, her mother Galina Ivanovna, and my wife's younger sister, Katya. That same Katya, who had been sunbathing in a micro-bikini on the beach this whole time, laughed too loudly next to me and seemed to accidentally brush my back as she passed. Twenty-three years old, a seven-year age difference with Marina, and as if from another universe: uninhibited, with a daring gaze and a constant half-smile. The compartment smelled of old wood. We'd already been driving for six hours; the black silhouettes of trees flashed past the window, occasionally catching a glimpse of a lighted window in a small house. My wife and mother-in-law were already snoring evenly on the upper berths. Marina snored softly, breathing out. My mother-in-law was emitting such a powerful roar that the windows rattled. I lay on the lower berth by the window, Katya on the opposite lower berth, facing me. Between us was a small table with the remains of dinner. I wasn't sleeping. It wasn't just the snoring that was to blame. I saw Katya tossing and turning under her blanket. The moonlight filtering through the curtain picked out the outline of her hip, shoulder, and neck from the darkness. She lay on her side, looking at me. I pretended to be asleep, but I felt her gaze on my skin, like a physical touch. "Are you sleeping?" Her whisper was barely audible, accompanied by snoring. I paused, pretending to wake up. “No,” I muttered. “I can’t sleep.” "Me too," she shifted, the blanket slipping slightly, revealing her shoulder. She was wearing only a T-shirt and, judging by the look of it, panties. "It's stuffy." — Open the window. "Are you afraid I'll lose?" a familiar playful note could be heard in her voice. I chuckled in the darkness. — I'm afraid your mother will wake up and start giving you a lecture about drafts. Katya snorted quietly. "She's sleeping like a log. And Marina, too. How can they pass out like that? We're on a train, it's an adventure." "They're tired," I said, though I knew it wasn't because they were tired. They were simply bored. And Katya... Katya seemed to feed off the very atmosphere—dark, cramped, mysterious. There was a pause. The only sounds were the clatter of wheels and snoring. "Aren't you bored?" she whispered again. - A little. "Want me to tell you something interesting?" She rolled over onto her back, and I saw the curves of her braless breasts clearly outlined beneath the thin fabric of her T-shirt. I looked away, but it was too late—the blood had already begun to rush to the wrong places. - For example? “For example,” she turned to face me again, propping her head up with her hand, “I saw the way you looked at me today when I was coming out of the sea. It was like I was struck by an electric shock. - I don't… "Don't lie," she interrupted softly. "I saw it. And you know what? I liked it." My heart started pounding so loudly it seemed audible even above the clatter of the wheels. It was that very line we'd never crossed during our entire vacation—glances, casual touches, ambiguous jokes. But now, in the darkness of the compartment, under the cover of the night and the snoring of relatives, that line melted away like smoke. "Katya, this isn't..." I began, but the words stuck in my throat. Because a part of me—the one below the waist—was screaming "yes." “Not what? Not right? Inappropriate?” she whispered, her voice becoming even quieter, even more intimate. “Who will know? They’re asleep. And we… we’ll just flirt a little. So it won’t be boring.” I felt a shiver run through me. The offer was clear, albeit veiled. I should have refused. I should have turned to the wall and pretended to sleep. But I lay there, paralyzed by a mixture of fear and arousal. "And how do you imagine this flirting?" I breathed out, already hating myself for this question. I saw her teeth flash in the darkness as she smiled. — For starters… we could shorten the distance. It's cramped here, isn't it? And before I could say anything, she slid silently off her bunk. Barefoot, wearing only a T-shirt and panties, which I could now see—dark, lacy, low on her hips. She sat down on the edge of my bunk, so close that her knee touched my thigh under the blanket. "Aren't you cold?" I asked in a stupid, choked voice. “It’s going to get hot,” she said simply, placing her palm on my chest over the blanket. Her touch burned. I froze. Her hand was small and warm, and she slowly moved her palm over my chest. I was wearing shorts and a T-shirt, and through the thin fabric I felt every movement of her fingers. “Katya…” my warning sounded weak. “Quiet,” she put her finger to my lips. “They’re sleeping. Relax.” She pulled back the edge of my blanket and, without invitation, slid under it with a smooth movement, ending up next to me on the narrow berth. We lay side by side, her body pressed against me with its warm, flexible contour. I felt her breasts pressed against my side, her hips, her bare skin. "That's better," she whispered right into my ear, her breath burning me. "Much more comfortable." I was hard with excitement. My cock, already semi-erect from her play, was now completely hard, pressing against the fabric of my shorts. Katya must have felt it. She pressed her hip against it and sighed softly. "Wow..." her whisper was full of approval. "I knew you weren't as boring as you pretended to be." Her hand slid from my chest to my stomach, her fingers slipping under the elastic of my shorts. I grabbed her wrist. - Stop. We can't. “Why?” She didn’t resist, just looked at me in the semi-darkness. Her eyes were huge and dark. “No one sees. No one will know. It’s our little secret. Don’t you want it?” She said it so casually, as if she were asking if I wanted some tea. And that was her whole flirtation—direct, brazen, devoid of false modesty. And damn, it worked. My grip on her wrist loosened. “This is wrong,” I muttered, the last bastion of my conscience. "It's a turn-on," she corrected, pulling her hand away and placing her palm directly on my hard cock through the fabric of my shorts. She grabbed it and squeezed. I groaned. Quietly, subduedly, but it was a groan. Katya immediately covered my mouth with her free hand. "Quiet, quiet... Control yourself. We don't want to wake them, do we? Imagine what will happen if Marina wakes up now." The very thought, terrifying and vicious at the same time, made my cock throb in her hand. Katya felt it and grinned. — Are you afraid? Or... on the contrary, do you like it? She began to slowly massage me through the fabric, her fingers tracing the shape of my shaft, the head. I closed my eyes. It was over. I gave in. I wanted this. I wanted her. Here and now. “Take off your shorts,” she ordered in a whisper, her voice losing its playfulness and taking on a commanding, greedy edge. I helped her by lifting my hips, and she pulled my shorts and underwear down in one motion. My cock sprang out, hard, tense, already slightly wet at the tip. Katya gasped with pleasure. “Beautiful…” she whispered and immediately leaned over, taking him into her mouth. I bit my fist to keep from screaming. Her lips were hot and wet, her tongue wrapped around my shaft, and her head began to move rhythmically. She sucked greedily, with wet, loud sounds that were drowned out by the clatter of the wheels. I looked at her dark head between my legs, at the way her cheeks were sucked in, and I thought I was going to go crazy. She worked her mouth, holding my base with one hand, and with the other she reached under her T-shirt and caressed her own breast. The sight was so depraved, so forbidden, that the blood pounded in my temples. She pulled away from my cock with a loud smack, wiped her lips with the back of her hand and looked at me. — Do you want more? I just nodded, unable to utter a word. - Then move over. I pressed myself against the wall, and Katya climbed on top of me, kneeling between my legs. She pulled her T-shirt over her head. In the moonlight, her body was pale and perfect: small, firm breasts with dark, swollen nipples, a slender waist, the soft curve of her hips. She also removed those very same lace panties, simply pulling them down and tossing them somewhere into the darkness. "It's all wet from you," she said simply, running her hand between her legs. "And from my thoughts, too." She rose up on her knees, parted her labia with one hand, and guided my penis to her entrance with the other. I saw everything: the dark triangle of pubic hair, the pink slit, glistening with arousal. She lowered herself onto me slowly, with a quiet, drawn-out exhalation. She was tight. Incredibly tight and scorchingly wet inside. I entered her completely, and she froze, sitting on me, taking my cock completely inside her. “Oh God…” she blurted out. “It feels so good.” She placed her hands on my chest for support and began to move. Slowly, smoothly, raising and lowering her hips. Her inner muscles gripped me, squeezing, sliding along my entire length. I stared at her, mesmerized: at the way her breasts swayed in rhythm with her movements, the way her face contorted with pleasure, the way she bit her lower lip to keep from moaning too loudly. “Yes… like that…” she muttered, picking up the pace. “Oh, fuck, yes…” I grabbed her hips, helping her, setting the rhythm. Our bodies slapped together with every movement, but the sound was drowned out by the general hum of the train. She leaned toward me, and her breasts were against my face. I took one nipple into my mouth, sucking and nibbling. Katya moaned right into my ear, her breathing becoming ragged. "I'm cumming... I'm going to cum..." she whispered, and her inner muscles spasmed around my cock. She shook all over, pressing herself against me, her nails digging into my shoulders. The orgasm rolled through her in a long, shaking wave. She buried her face in my neck, muffling her growling moans. As her contractions began to weaken, she raised her head. Her face was wet with tears and sweat, but she smiled a victorious, predatory smile. "Now you," she whispered and began moving again, faster, more insistently. She didn't give me time to come to my senses, her still wet, sensitive insides squeezing me with renewed vigor. "Cum inside me. I want you to cum inside me." “You can’t…” burst out of me. The last vestige of reason. “You can!” She leaned over, and her lips almost touched mine. “No one will know. Finish. Give me all your cum.” Her words, her brazenness, her body—all of it shattered the last barriers. I felt a wave building at the base of my spine, a tightening inside me. I dug my fingers into her buttocks, pulled her close, and thrust all the way inside her at the moment of climax. The orgasm erupted from me in a long, powerful pulsation. I felt my seed burst forth and fill her, hot and abundant. Katya moaned again, her body shaking with a second, weaker orgasm, triggered by mine. We lay motionless, fused together, listening to our hearts beat. She was still sitting on me, my cock gradually losing its hardness inside her. I felt our mixture of fluids leak out of her and drip onto the sheet beneath me. Katya was the first to come to her senses. She slowly, reluctantly, rose from me, and I felt my cock, wet and sticky, slip out of her. She reached for her panties, found them, but didn't put them on, instead simply wiping them between her legs and then tossing them into the far corner. “Evidence,” she grinned and put on just a T-shirt again. She lay down next to me, snuggled close, her head resting on my shoulder. We lay there, listening to the snoring and the clatter of the wheels. Reality slowly began to return. Dirty, treacherous reality. “What now?” I asked quietly. "What? It's okay," she ran her hand over my chest. "We had a good time. And no one got hurt." - Marina... "Marina's asleep," Katya said her sister's name so easily, as if she weren't her family member, but just another passenger on the train. "And she won't know. Never. It will stay here, in this compartment. Our little secret." But in her voice I heard not a promise, but a challenge. And anticipation. This wasn't a one-time deal. She was already looking ahead, planning the next meeting, the next opportunity. I felt guilty. I had just cheated on my wife with her sister, three meters away from her. I came inside her sister. Katya stood up and kissed me on the lips. A long, wet, possessive kiss in which I could taste myself and her. “Sleep,” she said, and as silently as she had come, she slid back onto her bunk. I lay there, staring at the ceiling. It smelled of sex. My wife was snoring upstairs. Across from me, covered with a blanket, lay her sister, who had just ridden me to orgasm. I expected to be overwhelmed with remorse. To hate myself. But instead, I felt only emptiness and a strange, unpleasant arousal that refused to go away. And I knew that when the train stopped and we stepped out onto the platform, I would look at Katya, and she would look at me. And there would be this secret between us. A dirty, hot, dangerous secret. And the train carried us further into the night, the clatter of its wheels beating out the rhythm of our betrayal.