Quest For the Moon Rock

A group of four fairies, masters of illusion magic, trapped in the human world for the last few thousand years, seek a way back to their own world. There is a spell that opens a gateway, but they have as of yet been unable to get hold of one of the most vital ingredients of this spell: a piece of genuine moon rock.

Fortunately, a small group of humans managed to use technology to do what magic couldn't: not only did they go to the moon, but they also returned, bringing with them samples of moon rock. One such sample is resting in a nearby museum.

The spell can only be completed in the light of the first full moon after midsummer's day. That's tonight.

The humans don't know the magical potency of what they have. To them, it's just a curiosity. Surely it can't be all that heavily guarded... right?