Enter Doyle, part one, Chapter 1b; Steampunked, part 2.
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Doyle pulled the cloth off of the object on the stage, revealing a box festooned with gears and pipes, its lid laying haphazardly on the top. "No peeking inside yet, Mirian."
He stepped back, and picked up the lid. "Get in," he told Mirian a little gruffly. She complied, looking at the people watching from below the stage.
"Now you may notice there's no latches or bolts on the outside of this box. That's by design. Once I put the lid on, it locks down, and the only way to open it again is from the inside." He looked at Mirian. "Wave goodbye, Miri."
The young woman looked around at the audience carefully, her eyes meeting with one or two people, then she waved, smiled, and crouched down inside the box.
Doyle placed the lid in position. There was a loud latching sound as it slid into place.
"So, now it's up to Mirian. She figures out the puzzle and opens the box. Or that's the last we see of Miri..."
"Hello?..." The woman's voice came over the speakers.
Doyle smiled. "Oh yeah. Since watching a box is boring, I've equipped her with a mic so she can tell you what's happening as she tries to get out." And with that, he walked off the stage, leaving the spectators to their drinks and chat as they watched the box.