The Lie Detector

"What's that?" Sienna asked, spotting the metal case in her brother's hand. She sat up straighter. Her online lectures were done for the day and she was thankful for a distraction.

"None of your business squirt," Callum replied. He set the case down on the table and walked over to the coffee machine. Switching it on before turning and resting his ass on the kitchen side, facing his sister.

"Don't call me that!" she whined, then immediately regretted her tone. She always tried desperately to not let him get to her. She took a deep breath. "Seriously though, what is it?" She ran her fingers through her long blonde hair, well, almost blonde, her dark roots starting to show through. She knew she needed to sort that out.

"Something from work we've been working on," Callum said. "I wanted to try it out over the weekend." He waited for his coffee, glad it was Friday at last. It had been a tough week and he needed to unwind. He still had a bit of work to finish, nothing too taxing, a bit of testing, and then he could do whatever he wanted.

"I was hoping for your help actually," he added. He watched his sister look up and stare at him suspiciously.

"With what?" she asked.

"I've been working on a lie detector," he said, his eyes flicking to the case. "It's supposed to be unbeatable. I'm pretty confident in it, but it needs more testing."

Sienna thought for a second, her brain addled by her lectures. She decided it would be a laugh.

"I'll do it, if you go on it after, and I ask you questions," Sienna said, losing herself slightly in his bright green eyes.

Callum thought hard, he knew how good the machine was. He didn't see any harm though, and it was a good test. "Okay," he agreed.

"Yes!" Sienna said, excited. She jumped up. "I'll just get dressed." She hurried out the room and Callum watched her go, his eyes falling to her slender legs beneath the white baggy t-shirt she was wearing. It was long and looked like she had nothing on her bottom half. Maybe she didn't, he thought. He shook his head and turned to finish making his coffee.

"She's grown up," he muttered. Shame trickling through him. His younger sister wants 18 now, and had grown into a very attractive young woman. He shook his head again.

Callum was sitting at the table when Sienna came back in. It took every ounce of his self control not to look over her body.He knew what she was wearing, having checked her out plenty of times in it.

Sienna smiled inside as she watched the inner struggle of her brother. She knew the black leggings she wore and the blue crop top made him uncomfortable. It showed plenty of skin and highlighted her perfect slender body and firm round breasts. She knew it was wrong, but there was something about the glances he gave her that made her feel good. Wrong, but good. There was no harm in a few fantasies, she thought.

"I'll just get a drink," she said. Callum took in her body again. The tight leggings highlighting her long slender legs and perfect round ass. They were low on her hips and her ribs tightened her skin as she reached for a glass. Her thin, toned waist visible beneath her crop top.

Sienna poured herself some juice and went over to the table. She plonked herself down into the chair opposite her brother.

"Where do we start?" she asked. She was glad their parents were out. It was always nice to spend time with her brother. There wasn't enough of him lately, what with her studying and his work. She missed him.

They had always got on. The occasional brother and sister argument, but generally they enjoyed each other's company. And he's quite easy on the eye, Sienna thought. His short, perfectly styled blonde hair. His naturally lighter. His handsome features and an athletic physique. He was just over 6 feet, so had quite a few inches on her. Which she liked in her men.

She watched him stand and put the metal case on the table. He opened it and took out a small black box, pressing a button that made a blue light come on. He looked good in his work stuff. Smart trousers and a blue shirt.

Callum moved and stood above his sister and brushed her hair behind her ear, noticing the shiver that ran down her spine. He attached a small node to her temple. His eyes drifted to her cleavage, her firm breasts pushed together in the V of her top

"It's not very big," Sienna said, looking up. Callum nearly jumped and pulled his eyes away. Looking into hers. Recovering nicely.

"Size isn't everything," Callum said, smiling. He winked.

"Ew gross," Sienna said. "Number one in the top ten things you never want your brother to say. And the wink just made me sick a bit in my mouth."

Callum laughed. "Now sit still whilst I calibrate it." He started pressing buttons and turning dials.

"Is it a yes and no jobby?" Sienna asked, starting to feel nervous. She wondered why she agreed to this. There were certain secrets in her head that maybe she didn't want to reveal to her brother. No scratch that, definitely didn't want to reveal.

"No. It can read whole sentences," said Callum. "That's what makes this new one so special." He pressed a button and it hummed gently to life.

"Oh that's good," Sienna said, nervously. The computer made a sound like you get when you answer a question wrong on a game show. EEH EEH.

"Your first lie," Callum said, grinning. "Starting to feel nervous, Squirt?"

"No!" she said. The same noise. Callum laughed. "Oh for fucks sake." She had definitely made a mistake here.

"Okay. Let's start," Callum said. "Some obvious questions first to just check if it's working. Is your name Beryl?"

"No. My name isn't Beryl," she said. The computer went ping, the truth.

"Are you a pygmy goat?" Callum said, grinning.

"Yes I am," Sienna laughed. He knew she liked pygmy goats. EEH EEH. "Phew. That would have been a shock.

"Am I your brother?" Callum asked.

"Unfortunately you are," Sienna joked. Trying not to use yes. She wanted to see how good this thing really was. PING.

"Good," Callum said. He leant back in his chair, thinking.

"Don't be mean," Sienna said. "Remember I'm helping you."

Callum smiled. "Wouldn't dream of it," he said. He leaned forward. "Do you like my art work?"

Sienna laughed. "Dickhead," she said. "Yes I do." The machine pinged. The truth. "After some praise are you.

Callum smiled. "Just checking you weren't just being nice," he said. He liked to sketch and sometimes paint in his spare time. Sierra always encouraged him, he just wanted to make sure she wasn't being kind when she said they were good. "Thank you."

"Have you ever stolen anything?" he said, a quick change to catch her off guard.

Sienna stuttered. Blushed. She decided it was best to tell the truth. "When I was 8 I stuck a pink pencil into my coat pocket," she said. "It was in the old local shop. I've felt guilty ever since."

Callum laughed. "You rebel," he said. "I promise not to report you."

"Hey. I'm a good girl," Sienna said. "That moment was a blip in my honest and flawless personality." She smiled sweetly and Callum admired her pretty features.

"I'm sure there's some darkness in there somewhere," Callum said. "You can't be all sweetness and light."

Sienna dramatically placed her hand over her heart, almost cupping her firm round breasts. Callum couldn't help but look,and looking back up quickly.

"How could you say such a thing?" Sienna replied, just as dramatically as her pose.

Callum thought hard. There must be something on her he thought. Too many inappropriate questions flooding his mind.

"Do you have a boyfriend?" he asked. This was the least inappropriate he could think of.

"Bit personal," she muttered. "No I don't." The machine pinged.

Callum felt a strange sense of relief at the truthful answer. He then realised an error.

"Girlfriend?" he asked. His sister's eyes narrowed.

"No," she said. The machine pinged. "I am not romantically involved with anyone." If he asked a few weeks ago it might have been a different noise from the lie detector. Her recent relationship, with a guy, had ended a bit messily. The usual, he wanted more, but she wasn't ready for that kind of commitment from him. She was disappointed because the sex had been good. She remembered it fondly and felt a stir in her lower abdomen. It had been a while since then.

"Your love of Justin Bieber scare them off?" Callum said, laughing.

"Fuck you," Sienna said. She gave him the finger. That was years ago but she knew he loved teasing her.

"You wish," Callum said. An automatic response.

"Yeah right," Sienna started, forgetting she had the lie detector on for a second. "I wouldn't want to go anywhere near you." EEH EEH. The computer highlighted the lie instantly. Sienna blushed. Callum gave a sly smile. Interesting, he thought.

He knew it was wrong but he couldn't help embarrassing his sister, time to step things up. "How often do you masturbate?" he said.

Sienna's mouth opened in shock. "Never!" she said, not thinking again. Her mouth went into defensive mode. The lie tone. "Well, I might do it occasionally." EEH EEH. Callum laughed.

"Tell the truth now sis," Callum said. A big grin on his face.

"I'm not answering that," Sienna said, defiantly.

"Remember you get your own back after," Callum said. Now feeling slightly worried about pushing his sister too much. It would be worth it though, he thought.

Sienna considered this, and thought too that it would be worth it. How bad could his questions get? And she was sure her self pleasuring was pretty normal.

"Most days," she said quietly. The machine pinged.

"What was that sis?" Callum asked, he had heard her perfectly, but was enjoying making her squirm.

"I play with myself nearly everyday," she shouted, the machine pinged again.

"That's quite a lot," Callum laughed.

"Not as much as you," Sienna said. "I hear you all the time, your bed banging the wall." Callum's smile dropped off his face. A ping.

"Well you shouldn't be listening," he said sulkily.

"Well I don't listen on purpose," Sienna said, the computer spotted the lie. She flushed red. Callum grinned.

"So you listen to me wanking then?" he asked. He felt his cock hardening in his trousers, he knew he shouldn't whilst talking about this stuff with his sister, but he couldn't help it.

"It's hard to ignore," she replied, looking down at the table. PING. The truth. "Can we change the subject?" She too was starting to feel aroused by this conversation.

"Not yet," Callum said.

"Have you ever fantasised about a family member when you play with yourself?" Callum said.

"Ew gross! No way, " Sienna said. EEH EEH. "No fucking way, that things rigged, or you're pressing the buttons." She crossed her arms hoping he believed her. She knew she was lying though. Callum ignored her.

"Is it dad?" Callum asked.

"No," Sierra said, knowing what was coming. EEH EEH. She flushed bright pink.

"Holy shit," Callum said. "Mum?"

"No, definitely not," Sienna nearly shouted. "And if that thing fucking says anything different." It pinged. Relief washed over Sierra, she wasn't interested in women.

"What were you doing with dad?" Callum asked.

"Were you fucking him in your fantasies whilst getting off?" he asked.

"None of your fucking business," Sienna said. The tone in her voice itself was answer enough for Callum to leave that one alone, but he needed to know something else.

"Do you ever fantasise about me?" he asked.

"God no!" Sienna answered, almost shouting. As soon as it left her lips, she cringed. EEH EEH.

Callum smirked, finding it hilarious, but he couldn't deny it turned him on, the hardening in his underwear proved that point.

"What do you fantasise about?" Callum asked. "What do we get up to?" His sister had an amazing pink glow in her cheeks. He couldn't help but find it incredibly cute.

She knew how screwed she was hooked up to the bastard lie detector. The emotions running through her body screwed with her self control. She decided to just come out with it.

"It's only a fantasy," she said. "It's too weird to be real, but I can't help it. Sometimes I want........." She paused. "Think......what it would be like to have sex." The machine pinged.

Callum nearly choked, but kept it well hidden. Holy fuck, he thought. He had definitely had those thoughts himself, but he was a horny teenage boy with a hot sister. He never imagined she felt the same way. This had escalated way too quickly.

"Are you thinking about it now?" he asked.

"No," Sienna said quietly. EEH EEH. "For fucks sake." She was flustered now, the rising heat between her thighs making it hard to concentrate. Callum's studying gaze wasn't helping.

"Are you turned on now?" Callum said. She didn't answer, but he could see she was. He knew because of how turned on he was.

"Do you want to touch yourself?" Callum asked. His cock now raging in his jeans. He looked at his sister's flushed face.

"No," Sienna said, quietly. Callum didn't need the machine to tell him it was a lie, but it did. Sienna let out a soft moan, her hand was on her inside thigh, so close.

"Touch yourself," Callum instructed.

"It's wrong," she said, quietly.

"I know you want to," he said. "I want to see it."

Sienna couldn't stop herself from obeying him as her hand went between her legs, she moaned. She pushed the fabric of her crotch into herself. Her leggings pushed her panties into herself, wetting them further.

"Does it feel good?" Callum asked. He couldn't see what she was doing under the table, but he could imagine, and it turned him on a lot.

"Really good," Sienna said, pushing harder and slowly rubbing. PING. The truth. She moaned.

She's so pretty, Callum thought, enjoying how much his sister had grown into a gorgeous young woman. He couldn't see what she was doing, but just seeing the expression on her face was hot enough.

Sienna rubbed herself harder through her leggings, her arousal growing quickly. The thought of her brother opposite was intoxicating. She moved up to her waistband, easing her hand in.

Sienna's hand slid inside her leggings and underwear, between her legs, and her fingers between her moist engorged lips. She pushed two into her and groaned again. She watched Callum watching her, knowing she should stop, but couldn't. She was close to cumming already. She touched her clit and groaned again.

"Do you want to cum?" Callum asked, rubbing his hard cock through his trousers, under the table. She looked so amazing, he thought. Her face was beautiful as she writhed on her fingers.

"God yes," she moaned. The lie detector told them this was true, but it was pretty obvious. She was sure he was touching himself too. Getting off on her. She worked her fingers faster, so close.

She kept her eyes on him as she played with herself. The fact he was watching her so intently turned her on further. Being watched was another fantasy of hers. She groaned loudly. She wondered how hard he was for her. How big?

A strong wave of pure bliss hit her as she moved her fingers slightly, squeezing her clit between them as they rose in tempo slightly. She squeezed a breast through her top.

"Oh fuck," she groaned. Her eyes rolling and biting her lip. It came on quickly.

She cried out in pleasure as she orgasmed into her leggings, her fingers working a bit more before pushing into herself and holding on. Her body shook in the chair and she slid slowly down, before grabbing hold of the table with her free hand.

"Holy shit," Callum muttered. His cock raging to be free and touched. He couldn't take his eyes off her as she sat there quaking with her eyes closed. He had never seen anything so beautiful. Her body spasmed and twitched. Her breasts heaving.

"I shouldn't have done that," she muttered after a while. "That was your fault." She took her fingers out, they glistened with her juices. She unsteadily stood up. Callum looked at her thin legs in her leggings, her crotch darker with the dampness.

She pulled the node off her temple and placed it on the table, wondering why she hadn't done that earlier.

"Don't fucking go anywhere," she added. "Your turn next." She unsteadily left the room.

Callum rearranged the raging hard penis straining in his shorts and boxers. Trying to sort it into a less obvious and more comfortable position. Touching it didn't help the situation though. Watching Sienna cum had made him incredibly horny. He sat there uncomfortably.

After a short while Sienna came back. She'd changed her leggings and was now wearing a short summery dress. Light blue with delicate small white flowers. Thin straps and a plunging neckline. Again showing off her impressive cleavage. Callum eyed her perfect slender legs.

"Let's forget that ever happened," she grumbled, plonking herself back down in her chair. She knew that would never happen. She even wanted more. She forced the feeling back down, but she couldn't deny that fact she had put on her best knickers just in case.

Not fucking likely, Callum thought. "Okay," he said.

"Your go," Sienna said.

"Okay," Callum replied. Part of him wanted to try and get out of it, but the semi hard cock twitching in his underwear wanted to see what happened next.

He picked up the sensor and put it on his temple.

"Do some obvious questions first," he suggested. "Check it's working."

"Okay," Sienna said, thinking. "What's your name?"

"Callum," Callum replied. The machine pinged.

"Correct," Sienna said, smiling. Callum wasn't sure he trusted that grin. "Well done."

"Patronising much?" Callum said, laughing.

"Do you have a sister named Sienna?" she asked.

"Yes," Callum said. PING.

"Is she awesome?" Sienna said, grinning.

"No," Callum said. Laughing. EEH EEH.

They both laughed. "Well we know it works," Sienna said. "Let's get this show on the road. She sat up straighter, ready for business. Callum squirmed slightly. He was still sporting an erection from earlier.

"How many girls have you had sex with?" Sienna asked. BANG, she thought, make him squirm even more.

"Nine," he answered. The machine confirmed the truth.

"Slut," she said. Laughing.

"Fuck off," he said. "How many have you slept with?"

"Too late bro," she said. "My turn now." She was glad he hadn't asked. It was only 4 and most of them had been disappointingly quick.

Callum cursed himself for not asking the obvious questions.

"Okay let's begin properly," Callum said. Trying to change the subject.

"Okay," she said. A sly little smirk crossing her pretty features.

"Let's keep it clean," Callum said. Grimacing at what was coming.

She hit him hard and fast. "Did you give my My Little Pony to Barney when we were younger?" Sienna said.

"Jesus sis," Callum laughed.

"Answer it." Sienna said, smiling. They had been a lot younger when their dog Barney had chewed up her favourite My Little Pony. Sienna was adamant she had left her high on her shelf and had always been pretty sure her brother had given it to the dog. Their parents had never believed her. She had gotten over it, but it had always annoyed her that Callum had never confessed.

"It wasn't me," Callum said. The machine highlighted the lie. "Fucking things playing up." He gave the machine a light bang with his fist.

Sienna scowled at him. "I fucking knew it," she said, coldly. "I knew you were fucking Lying."

"You ate the last Frube," he said. "I was angry." He tried to stay serious but the corners of his mouth turned up.

"Don't you fucking laugh," Sienna said. "This is serious. I loved that Pony. Pinkie Pie was my favourite."

The comment tipped him over the edge and he burst out laughing. Sienna joined him. Callum laughed so hard that tears ran down his face. It took a while for both of them to gain control.

"Prick," Sienna said. "You will pay for that."