Note: This story was dynamically reformatted for online reading convenience.
 
 If I told you that I hadn't noticed how sexy Rosie, my wife's sister, was I
would be lying.  From the day I met her, three years ago, I had jerked of
too many times imagining my cock pumping in and out of her lovely lips and,
I assume, lovely cunt.  Linda, my wife, is quite sexy too.  But next to her
younger sister, she is a plain Jane.  Rosie, like my wife, was short at
about 5'3".  She had a fabulous body that she kept toned through constant
workouts.  In this respect, she differed from my wife who had let herself
go and, although you couldn't call her fat, she wasn't fit either.  Then
there were the knockers.  Linda's were big, but Rosie's were huge.  So when
my wife announced that Rosie had found a job in our city and would be
moving in with us, I was excited.  The first few months after she moved in,
she didn't disappoint.  She would walk around the house clothed in almost
nothing and I had to start wearing underwear under my jockeys to hide my
perpetual hard-on.  One day, she was working in the kitchen and I had to
pass her to get to the fridge.  I cannot honestly tell you that I brushed
my crotch against her ass accidentally.  On the other hand, I cant be sure
I did it knowingly either.  It just happened and when it did, an electric
shock ran through me.  On one hand, I was excited.  On the other, I was
scared about her reaction.  But she just turned and smiled at me.  Nothing
was said.  So when I passed her on my way back, I rubbed against her
knowingly.  Once more, she turned to me and smiled.  At that moment, I
began to harbour thoughts that this might actually happen.  A few more
months later, Linda's mother fell ill.  Since Rosie had just joined her
job, she was not able to take time off.  So it was decided that Linda would
go to care for their mom, while Rosie stayed behind.  After we dropped
Linda at the airport, Rosie got into the front seat.  She was wearing a
pair of hot pants which left her thighs exposed and very close to my hand
that was on the gear shift.  Although I didn't need to keep my hand on the
stick, I left it there.  After a few minutes, I felt her skin against my
fingers.  I looked down and noticed that she was resting her leg against my
hand.  I looked at her.  She smiled at me.  "I've always wanted to sit here
next to you.  But with Linda around, that was never possible.  Now I have
you for me until she is back." Although the air-conditioner was running
full blast, I could feel the sweat on my forehead and under my collar. 
"What do you mean?" I asked her.  "Well, as the younger child, it is my
duty to go take care of my parents.  But Linda has gone in my place.  So
when she is not here to do her duty as your wife, isn't it only right that
I perform her duties?" With this, I felt her hand over my crotch.  "Oooh!
Is that for me?" I couldn't think of a smart reply as she tugged at my
belt, undid it, and then undid my trousers.  It was hard, but we finally
got my trousers down to my knees.  Then she undid her seat belt and climbed
on to her seat.  She then bent forward and took my penis in her mouth.  It
was amazing.  A long-held dream come true.  "Don't come below a hundred",
she told me.  "If you do, I will stop." I pressed my foot on the pedal and
watched the speed cross a hundred.  On my lap, my sexy sister-in-law sucked
me like her life depended on it.  It didn't take me long to cum.  Soon I
was shooting my cum into her mouth and she took all that I had to give. 
After she cleaned me, she sat back and I pulled over.  After I had put my
trousers back on, we resumed our journey home.  Along the way, she told me
all the things she would do to me when we got back.  Needless to say, I was
hard by the time we parked the car.  "Come!  Fuck me in the back seat", she
said after I had pulled into the garage.  She opened her door and standing
outside the car she pulled down her shorts and panties.  She then opened
the back door, crawled in and lay on her back.  "Come on.  Fuck me." I
didn't need another invitation.  I ran around the car to her side and
climbed in over her.  She was wet and I slid in easily.  After having just
cum in her mouth, I was able to fuck her long and hard without worrying
about cumming early.  I achieved a rhythm and held it.  She moved her cunt
in unison with me.  We were both thrashing against each other.  "Oh fuck!
I'm cumming!" I kept my the steady rhythm as felt her convulse under me. 
It was the most amazing feeling - to feel a woman cum under you.  I
couldn't hold back and I began to shoot my cum into her cunt.  After we
were done, we lay in silence.  I don't know about her, but I was satisfied
and refreshed.  My wife stayed at her mother's place for three weeks. 
Three wonderful weeks when Rosie made my every fantasy come true.