From the frontpage of the module:
In the City of Greyhawk, the Royal Opera House and the Grand Theatre are well-known rivals and, on occasion, scathing accusations are followed by open-street brawls. In continued disrepair, the opera house anticipates a new production will keep its doors open permanently. That is, until the Royal begins to experience a series of unfortunate events. The cause is none other than its rival bent on treachery. As the curtain rises and Act One set in motion - insults, street fights and a dagger in the back is just the beginning. A one-round Core adventure set in the Garden Quarter in the City of Greyhawk for characters 1 - 11 (APLs 2 - 8).
The module's front page is wrongly numbered asa COR7-20.