You are a student of Merlin, the magician. Your adventure starts in Merlin's cave, where Merlin is busily working on his latest spell to control the sun and the moon. All of a sudden, Merlin announces that he will make you the chief wizard of the land if you can find the legendary Moonstone.
'No problem', you think to yourself.
Hey, wait a minute. If this is so easy, then why didn't Merlin find the Moonstone himself? Hmmm...
Notes
This adventure was originally issued as a disk bonus with Page 6, issue 34, July/August 1988. The instructions are on p. 23. Note that the introductory screen says it was written in 1987, but it was not published until 1988.
Here there is a complete walkthrough video from the author.
https://www.youtube.com/watch?v=MorvZQCcYAQ