Go check on Rachel

I walk up the stairs and kept my eyes on my sister's door as I made it there. I peek inside, and what I saw next was almost mind-blowing! My sister was on all fours, butt naked, smirking as she looked back at me. "Doctor...?" she purred. I swallowed my saliva, nervous about her bringing up the past again. "I've got a problem. I feel hot..." She pretended to complain, toppling on the bed and rolling onto her back, coyly finishing, "Can you take my temperature? I can do it either way..." I should've just left her to her own fantasies, but I actually closed the door behind me. My dick took over my rational thinking again. As I moved towards her, her slow-moving legs slid up and down, and her arms laid on the mattress as she purred in anticipation.

"I... I don't want you getting sick," I said, half-believing that I was helping Rachel. I grabbed my pants, pulled them and my underwear down to let my manhood spring out. She had that twinkle in her eye when she saw how erect I was. "Now... open wide. Under your tongue." I move my dick to her mouth, and she opened it with contentment while closing her eyes. As much of it could fit, she began sucking on it, bobbing her head on it almost... lovingly. I stood there, ignoring all signals to get out before it was too late, and watching My. Own. Sister... giving me a blowjob. Her legs rubbed against each other as if trying not to move or masturbate while I 'checked her fever'. She hummed and moaned, and after 2 minutes, she pulled off, licking around the helmet and gave a half-suppressed laugh.

"I'm burning up..." she grinned, enjoying my taste. I tried fighting the sensations, but they chipped at my willpower, and I leaned my head back some as she kept blowing me. At that moment... I snapped. I began rocking my groin back and forth, thrusting my dick into her mouth as she sucked on it. This almost made her ****, but she didn't seem to care as she really seemed to be in heat! She finally put two fingers in her cunt, thrusting them in and out and rolling them inside, too. I felt like I was gonna blow any minute if she kept this up.