Heather was behaving very strangely when she got back from the club that night. She kept giving people very weird looks. She even licked her lips on occasion.

I asked her if she was ok.

“Yep, fine”, she said. “I’ve never felt better, actually…”

I could see something was up; her face seemed to be redder than usual, and she was drinking like a fish. Not alcohol; just fluids. She was obviously trying to purge something out of her system.

Whatever she tried, it didn’t work.

Excusing herself, saying she needed an early night as she had work in the morning, she went to bed. At least, that’s what we thought she did.

None of us stayed up long; we’d all tired ourselves out at the club.

Francine and Sally excused themselves and went home, thanking me for a fun evening. That left me to tidy up. I tool one look around, decided to do it in the morning, and headed for bed.

That was when I found Heather waiting for me in my bed, stark naked. Problems were, she was supposed to be straight, and we were sisters…

She pulled me into bed with her. I tried to stop her, but she slapped me then hung on harder, putting her hand between my legs.

“Come on! You know you want to!”, she said. “I’ve seen you looking at me; you haven’t had a good screw for ages.”

I tried again to pull away.

“Heather, it’s not right! I’m your sister, for fucks sake! That and I didn’t think you were into girls…”

“Tonight’s a night for surprises…”, she said. Then she put a finger inside me.

“No… stop…”, I moaned. “Don’t…”

She started pumping the finger up and down, then inserted a second…

“Damn you…!”, I moaned. “Stop…”

She kissed me.

“Come on; please. Do this for me; I need it as well.”

To my amazement, she started guiding my hand toward her vagina. I snatched it away.

“Fine!”, she said. “I’ll warm you up first.”

She bent down and started licking my clit. How the hell had she got so experienced in pleasuring women so quickly? She knew I was gay; I’d had a girlfriend in college. She also knew I hadn’t been seeing anyone for a while. But she was my sister…!

We had been making so much noise we hadn’t realised someone had come into the flat. The first either knew about it was the shriek from the doorway…

“Stop that right now! What the fuck are you doing!!”

Mum stood in the doorway, aghast.

“If you didn’t recognise what we’re doing, I’m worried about you”, said Heather. “Or, is it because you did recognise it?”

Heather then said something that made mum and I both gasp.

“Come on, there’s room for you too. You know you want it.”

With another shriek, mum came in and yanked Heather off of me, giving her a good hard slap in the process.

“Pull yourself together and take a cold shower!”, she cried. She then looked at me.

“Sara, I’m ashamed of you. I know you’re happy being gay, but there’s no need to experiment with your sister!”

“She came on to me!”, I wailed.

Mum suddenly found out how true that was. Heather had suddenly wrapped herself around her mum and kissed her.

“Come on, mum. You know you need it…!”

Mum had to lock Heather in her room in the end. She then came back and apologised to me.

“I see it wasn’t your fault, now”, she said, phoning for the doctor. “When did this come on…?”

“She was like it when we got back from the club”, I said. “She looked like she was coming down with something as soon as we got in, and she went to bed early, only it was my bed, not hers.”

“Sounds like someone has slipped her something at the club”, mum said. “I’d better ring the police as well.”

Doctor Lacey turned up first; she was a friend of the family and came as soon as she heard how worried mum was. She was let in to see Heather. We made the mistake of leaving her alone with her…

There was a shriek, and the doctor came flying out of Heather’s room, her clothes already in tatters.

“She frigging jumped me!”, she cried. “She was trying to screw the daylights out of me. I’ve never seen anything like it.”

“Come back! Please! I’m sorry! I’ll take it slower next time!”, came Heather’s voice from inside her room, followed by the sound of her crying…

Before we could stop her, mum went in. The door slammed shut, then there was a click. Heather had taken the key and locked it from the inside…

The police had to break down the door…

Heather was unconscious, still naked. Mum was now naked as well…

The police took Heather away, the doctor in attendance. Then mum kissed me…

This ‘affliction’, whatever it was, was obviously contagious.

Problem was, I hadn’t got the strength to fight off mum…

I’ve never been screwed so hard in my life; talk about having your brains fucked out…! How on earth did everyone affected get so good at sex…?

For some reason, it didn’t seem to affect me at all. I was quite happy to carry on being the victim, not the instigator. Also, the effects didn’t seem to last; if mum was any guide to go by, Heather should be waking up in hospital soon, feeling very sorry for herself and really embarrassed…

As if it had heard my thoughts, mum’s mobile rang. I answered it. A very contrite Heather asked if someone could pick her up…

I went to get her, after making sure mum was ok. I wasn’t going to let her drive just coming down from a high, whatever it was.

Heather was in tears as I met her.

“Sara, are you and mum ok?”, she asked, as soon as I met her.

“Yes, we are. You weren’t in control of yourself”, I said.

“I wasn’t, but, at the same time, I needed the ‘release’”, she said. “I haven’t felt so rested in ages.”

“That’s exactly what mum said”, I replied. “Can you remember at all when or where you might have been spiked? The police think someone slipped you something at the club, and some of it was still on your lips, which is why mum was affected.”

“But I kissed you, too, didn’t I?”, said Heather.

“True”, I replied. “I must be immune, or something.”

We heard later that there weren’t any other incidents like ours, which left us all wondering why Heather had been singled out.

We also thought that was the end of it.

Things seemed to go back to normal. Mum and Heather went back to work, and I went back to Uni.

I came home one night really knackered after a day where everything seemed to have gone wrong. Heather was in; she tried to cheer me up, but nothing worked. In the end, I went to bed early, still depressed.

I had a very erotic dream during the night; at least that’s what I thought it was, to start with. I was bound to the bed and gagged, and someone was screwing the daylights out of me with a strap-on.

That was when I woke up fully, and found it wasn’t a dream at all…

Heather was on top of me again, pumping away.

I was indeed tied to my bed and firmly gagged; I could only manage a quiet whimper. I was moaning and arching my back, though, as Heather vanished between my legs…

Heather was banging me as skilfully as mum had before. I climaxed and passed out, only dimly hearing the sound of mum entering the room…

When I next awoke, I was untied and ungagged, but covered in sweat, sagged back on my bed, with mum sitting on the end of it. She told me Heather was back in hospital again; they were thinking this time of sending her to a secure unit for closer observation.

Mum then just snuggled down next to me and fell asleep, as I dropped off as well…

Next morning, I awoke to find mum lying beside me, staring at me.

“You’re cute when you snore”, she said. She’d been there all night…

We both rolled out of bed, then raced each other to the bathroom. Mum beat me, so I put the kettle on and made the tea while she washed, then used it after she’d finished. We then both talked about Heather whilst seated round the breakfast table…

I hadn’t noticed that mum was watching me strangely again. She had been behaving a bit weirdly, I’ll admit, but I was enjoying her company too much to notice. Then she put a hand on my leg…

Here we go again…

After we’d ended up back in bed again, I put two and two together. It was me causing all the problems, somehow. I was the only common factor, now…

By then, I was two happy to care. Mum and I were tightly wrapped around each other in the ‘sixty-nine’ position in bed, and I was giving as good as I was getting…

Heather, meanwhile, had recovered again…

We decided the only solution to prove that I was the problem was to split up for a short period, and as I was possibly the source it was decided that I was the one who should be on their own for a while. Heather and mum went to stay with their Aunt Clara, and I got the flat to myself for a few days.

While this was going on, Doctor Lacey came in to check up on me. She said she was doing it as a friend of the family…

You guessed it. We ended up in bed together…

By then, I really didn’t care. It didn’t help at all that Doctor Lacey was a really attractive woman; a five-foot ten leggy blonde with a beautiful smile and breasts to match. She was an absolute monster in bed, too…

I tried to make a run for it, twice, and got dragged back in each time. She was insatiable. At the same time, she managed to tell me the other reason she had come to see me.

“It’s your fault, all of this”, she said. “But there’s no way you could have known or done anything about it. The virus that you’ve got causes your body to chuck out weird pheromones by the gallon. They’ve only just come across it in research labs; yours is the first case ‘out in the wild’ so to speak.”

She managed to crawl out of bed, at last, then gave me an injection.

“There. That should cure you, within a few hours.”

“Why didn’t you give it to me as soon as you came round?”, I asked.

“I needed a good screw, and I fancy you”, she replied…

We ended up back in bed, this time willingly.

It was my turn to vanish between her legs; soon, she was moaning her head off, loudly…!

We then wrapped ourselves around each other, and were still there when Heather and mum got back after their long weekend away…

“Hi, mum!”, I squeaked. “Meet my new girlfriend…!”

She just gave Doctor Lacey a good hard look…

Checks proved that I’d been cured; there were no more spontaneous bursts of randy women around me (except for Doctor Lacey, but she’s biased).

Mum and Heather both went back to normal, well, as normal as ever for them. I was very sheepish and contrite around them; they both forgave me, however. They also liked having Doctor Lacey as part of the extended family…