Back at Robotniks base, Sonic had just passed through the automatic sliding door. Robotnik was just sitting in his throne enjoying the view of the ocean through the looking glass.
Sonic walked up the stairs to Robotniks throne where he presented the Chaos emerald to him, "I have returned with the Chaos emerald my master." Sonic kneeled before Robotnik as he turned around in his throne and took the Chaos emerald from Sonic's hand.
"Good job, Sonic, you have done well." Robotnik placed the Chaos emerald inside a Chaos emerald case with seven individual holes for all of the emeralds. The case slid its door closed automatically when the emerald was locked in. Robotnik gestured for Sonic to rise from his kneeling position.
Sonic stood up and awaited further orders.
Robotnik pushed a button on his throne that made a round platform rise from the middle of the lab at the bottom of the stairs. The platform had railings and a little surprise for Sonic, "There's no need for you at the moment my dear hedgehog, please escape to your cell until told otherwise."
Sonic did as he was told. He walked down the stairs and stepped on the round platform. When he held onto the railings, leather straps opened through a tiny door of the railings and held his wrists in place so he couldn't escape. He didn't freak out of course until Robotnik pushed another button on a remote that controlled Sonic's mind. Sonic was now his normal self. He looked around and saw his hands strapped down to the railings, "What happened, what did you make me do?"
Robotnik showed Sonic the chaos emerald from his chair, "You did my biddings my little guinea pig." he laughed.
"You won't get away with this Eggman." Sonic threatened with teeth clenching.
"I already have." Robotnik pressed a button on his throne that made the round platform go down.
Sonic tried to break free of the leather straps but it was useless. The platform was now too low for Sonic to see Robotnik. A door closed above him that closed the gap between him and the lab above. The platform stopped and Sonic was now in a dark jail cell where he was trapped until Robotnik needed him again.
Robotnik sat in his throne again overlooking the ocean with his hands cupped together, "I must stay in cover. I cannot send him to look for chaos emeralds like this every second of every day. I have to do it at certain times so he won't draw suspicion from his friends."