[Faceman]

Load from entering the temple an do NOT attack it (also disable AI to prevent your party from auto-attacking).
Then either take your best healer and cast a good healing spell (like Heal Serious or Critical Wounds or even better Lay on Hands, don't bother with light wounds).
If you have no proper spells memorized go a little further there are two scrolls of serious healing stashed.
Do NOT attack, just wait, after 2 or 3 seconds the demo should dissolve and the avatar should appear.