From the back of the box:
The Evil Demons have taken control of The Lonesome Monk's childhood home in his absence. The neighbouring peasants, led by local boy Jason, have tried in vain to gain back power. Brave horsemen bring The Lonesome Monk back from the Crusade to lead the rebellion against The Evil Demons. When he catches sight of his valley The Lonesome Monk is enraged at the devastation caused by The Evil Demons. This is war!
You can now lead The Lonesome Monk through the labyrinths of The Monastery against The Evil Demons. Collect the hidden treasure en route, and use the Golden Keys to unlock the Doors of Destiny. Keep your eyes peeled for the secret passages. You too could walk through walls!