How to trigger the plot of the mysterious record stage in Hong Kong?

1. After you get to the alley in the Hong Kong mystery record, you can find the stage for the performance. Forget it, go on, find the fortune-telling place and find a ruby on the table.

2. Go back to the stage and interact with the objects here as shown by the arrow in the figure below. After Redjade was installed, the stage plot was triggered and a man jumped down from the upstairs.