Steven was sitting on the living room couch being masturbated by Jack while Tiff and I gently sucked on his nipples. The boys turned to kiss each other and Tiff ran her fingertips over one of my breasts. Steven was just about to orgasm, so I lowered my head from his nipple, ready to catch it in my mouth.

Unexpectedly, Samantha walked in, and she spoke before we knew she was there. 'What's all this, then?' We all turned to face her just as Steven spurted.

For many weeks, I'd been meeting these three wonderful classmates every week at Samantha's flat. She was the big sister of Jack, and she would let him and Steven use the place on a Friday night while she was out with her friends. Except we'd never met her because she didn't know they'd been sneaking Tiff and I around for a bit of fun for weeks. Up until now, we'd always managed to leave before she came back.

'You didn't tell me you had women around as well,' she continued, sounding amused rather than angry.

We were all naked, so we made to put at least our underwear back on, while Steven grabbed a tissue to wipe up.

'No need to cover up on my account. None of you have got bits I haven't seen before.' Even so, I still hurried to put on my bra. I'd never been referred to as a woman before, though, so that made me happy.

'Um...' said Jack, his erection bulging behind his underwear. 'What are you doing home? It's early.'

'Forgot my purse.'

'Oh. Right.'

She faced me and pointed at my face. 'You've got spunk on your cheek.'

Without thinking, I scooped it into my mouth.

'So how do you all know each other?'

Jack stuttered. I don't know what he was going to say, but Tiff took over. She told Samantha about our masturbation group at school after games class, while Steven and I chipped in with extra bits and pieces about what we did on a Friday. We told her we always started our sessions with solo masturbation, then moved on to pairs, then maybe something as a group, like just then.

By the end of the story, Samantha was lapping up every word we said. 'So are you going back to do games next year? Start it up again.'

'No,' I said, 'everybody dropped games the moment they could.'

'Except Jack,' added Tiff. 'He says he wants to own a gym one day.'

Jack hadn't contributed to this explanation, so Samantha turned to him. 'And what's your story?'

He said nothing.

'Why the secrecy? Why didn't you just tell me you had some charming women round?' She winked at us girls. 'You know you can tell me anything. I'm not mum.'

He said nothing but looked at a point on the floor.

'I knew they were gay though,' she said to us. 'They've always been cute together.'

'I'm not gay,' said Jack.

'Jack's gay and Steven swings both ways.'

Steven now also looked at the floor, seemingly in embarrassment.

'I'm a lesbian, out and proud. I've got gaydar. I know who bats for what team without seeing them wanking each other off.'

'You don't look like a lesbian.' I blurted out without thinking. For one moment, I thought she was going to throw us out. 'Sorry, sorry,' I added, 'I didn't think.'

'I know, I'm not butch; it just isn't me.' She turned back to the boys. 'And I see your condoms in the bin all the time, and little empty packets of lube. From what you've said, that's been going on longer than these ladies have been round.'

'You boys have sex?' I asked.

'They've never done it in front of us,' added Tiff.

It sounds obvious saying it now, but although I'd seen their gay interactions, I'd never actually thought about them going as far as penetration. I can't tell you how turned on that made me. In that moment, I felt as though my clit was showing as big a bulge in my underwear as Jack still had.

'Anyway,' said her little brother, jabbing fingers at Tiff and me, 'they do stuff together as well.'

Samantha smiled a little. 'Really? Are you a couple as well?'

'No no,' I said. 'I'm definitely into boys. We're just friends. We don't even kiss.'

'Which is a bit stupid,' added Tiff. 'I mean, we're best friends.'

'I don't kiss my best friend,' Samantha said. 'You're lucky to have someone to do things with.'

'Is she straight?' I asked. 'Your friend?'

'Nope, bigger rug-muncher than I am, but we don't see each other in that way.' A silence fell over everyone. 'Well, as long as you're having fun. I've got my purse now, so I guess I'll leave you lot to your little sex club. Enjoy, but leave the place tidy; that's all I ever ask.'

She walked to the door as if to leave the room, then hesitated and turned back to face us. She caught the eye of only the girls, alternating between us. 'That said, I don't suppose there's room for another woman in your group, maybe a certain twenty-year-old femme?'

'Eww,' said Jack, 'no, there's not.'

Still looking only at us, she said, 'Does it look like I'm talking to you?'

'No way, Sam. I'm not watching my sister... Do anything.'

'Masturbate? Is that the word you're looking for? We all do it, it's no big deal.'

'Not with your own family.'

'Kath and Michael had sex,' I said.

Samantha turned to me. 'Who's Kath and Michael?'

'Cousins we go to school with.'

'They didn't have sex,' said Jack. 'That was just a rumor.'

'Well, him and I are both as gay as they come, so I guarantee there'll be nothing between us. He doesn't even have to look at me if he doesn't want to.' Jack made a mime of vomiting. 'But it's my flat, I decide who comes here, and I happen to like your friends from what I've seen.'

Tiff brightened up. 'Yes, of course you can join us.'

I nodded enthusiastically, but I didn't say anything. I thought Tiff could at least kiss her instead of begging me to do it.

Samantha smiled again, 'It's a deal, then. Give me a few minutes; I need to phone my friends and say something came up tonight.' Tiff let out a little yelp of excitement.

'Then I'm not staying,' said Jack. That's incest.'

'It's not if you don't touch each other.'

I didn't hear what he mumbled in reply.

Samantha once again nearly left the room before asking, 'Oh, do you ladies use vibrators?'

Oh my God. We'd talked about wanting them so much. Tiff used an electric toothbrush sometimes, but I found the vibration wasn't strong enough. 'We're only seventeen,' I said simply.

As if reading our minds, she said, 'No problem. I've got some you can borrow just now. Come and take your pick.'

'Brilliant,' said Tiff, immediately standing up.

Samantha made eye contact again, but only with her. 'I think there's going to be a real buzz between us.'