The light in my sister's eyes started to die that day, and jack seemed to be enjoying himself far too much. I knew something was wrong immediately and started investigating, jack was great at hiding his illicit affairs from anybody who wasn't looking but for a student who was after the information he was an open book.
It took almost a week of blackmailing my sister with the footage of her orgasm to make her willing to let jack touch her, and that's what I had been waiting for. Our parents worked online primarily, but occasionally they would take business trips out to the main branch for training or important meetings, and this trip would be a long one, a full week. I realized that Jack had timed his plan well, but it also worked for my plan so I couldn't complain.
On the first night after our parents left my sister came down from her room wearing a long coat, she"decided" to hang out with some "friends" by this time I had a monitoring app on her phone so I would know if I had to stop what was going on, and I knew exactly what was up.
She met him in a park, I don't know if Jack had realized she was into showing herself off or if he was just doing his own thing, when she sat down next to him on the bench he asked her if she was following instructions, she looked around anxiously and opened the coat, revealing that she was nude underneath and soaking wet.
Jack smiled, his real smile, just a little too wide and terrifying, "so" he said" are you finally ready to jack me off?" My sister nodded.
this was already going further then I wanted but honestly I really didn't care, I had drawn a line in the sand, I had them together, I had them in a place and at a time where there is no good excuse for them to meet, now I just needed him to push the envelope with something exactly like this. I was recording on my phone so that I could stop this, but I had a knife on me, if he tried to take her to a private place or to do anything he couldn't take back I would stop him, but until then I needed to wait.
My sister was still stuck, his dick was disgusting to her, she didn't want to be within a mile of it let alone touch it, but she was turned on and using the fact that she had to save her transcript as a thread of logic to hold together the warring sides of her brain. She felt sick, and wet, and angry, and horny, and confused. I wanted to save her, but I couldn't until I had enough proof, a video with enough footage to prove what he had done, so I waited.
It took a good ten minutes before jack came, my sister was practically drooling at jack as he stood and zipped his fly "good girl" he smiled creepily again "next time we meet, I'll give you a choice, if you let me fuck you I'll let you cum" jack turned on his heel leaving my shell shocked sister in his wake. I smiled and kept a block ahead of her as she stumbled home, it was time.