From the PDF introduction:
The Barrow of the Moon Druid should, at first, appear to be a traditional 5-room dungeon adventure. If the player characters are successful in surviving the barrow, on the next full moon, it will become clear to the players that the barrow was indeed no mere 5-room dungeon, but rather an ominous curse.
From the Cover:
As your party travels the Old Road which cuts a path through the dangerous moorlands, you spy an old barrow sitting off in the distance. An old gnarled tree, the only tree to be seen on the moor, sits atop the barrow watching over the round door set back deep in the mound. What possible treasures lie within the barrow mound, the one said to be the burial location of the Moon Druid? Who within the party will be brave enough to enter The Barrow of the Moon Druid?