Mycroft was pacing. He was convinced that it had been weeks since he'd first been imprisoned in Eurus' cell in Sherrinford. He knew that it had been days, but he had no way of tracking the time. There were no clocks or windows and food seemed to be brought to him at completely random intervals. He ate what was brought to him, if reluctantly, and did as the guards ordered. He had no power in the high security cell and Eurus loved to remind him of that fact.
"I've made the effort to come and see you, big brother, but you haven't even noticed me." came Eurus' singsong voice from the other side of the glass.
Mycroft froze and looked up, realizing that he hadn't even seen her enter. How long had he been pacing for? He couldn't remember.
"Aren't you going to talk to me?" Eurus asked, "You haven't even complimented what I'm wearing."
"My suit?" Mycroft murmured in confusion as he looked over her through the glass. He'd been forced to change into loose prison clothing at gunpoint at some point in the last few days.
"That's right." Eurus laughed, "I had to get it re-tailored to fit, but it suits me, don't you think?"
"Why are you wearing it?" he asked with a frown.
"I wanted to look the part when I'm pretending to be you. It's such a shame that you didn't bring your umbrella." Eurus pouted, "That would have completed the look."
"How did you do this? I put new security measures in place to stop this from happening!" Mycroft shouted in frustration.
"It's simple really." Eurus replied, walking closer to the glass, "I'm the smart one, Mycroft."
"You won't be able to get away with this for long. Sherlock will notice my absence and my colleagues will want to meet with me in person." Mycroft hissed.
"Oh Mycroft, you really think that I've done this alone, don't you?" Eurus laughed, "The truth is so much worse than that."
Mycroft's eyes widened and his skin became very pale, "My colleagues know I'm here." he realized.
"Now you understand." Eurus said, clapping her hands, "Poor Mycroft, they've been planning to assassinate you for some time. You've become too big for your boots!"
"So instead of assassination, I am to be imprisoned?" Mycroft asked.
"MI6 still need you to solve puzzles for them." Eurus replied, "You're to be contained here for the foreseeable future. If you complete the puzzles, you might even get a reward."
"Don't use my own words against me!" Mycroft hissed, "You are mad, Eurus. It won't take them long to realize it and then you'll be back in a cell too!"
Eurus laughed, "Big brother, you're so slow!" she taunted, "I'm not free, I haven't been released. I've had you brought here as a playmate."
"But why? What do you gain from that?" Mycroft asked.
"I'm in control here, why would I give that up?" Eurus said, "I hope you enjoy your stay, Mycroft. When you feel the madness begin, you'll be better off just accepting it."
After Eurus had left, Mycroft sunk down to his knees. He was a prisoner now - trapped in a game of his own creation.