The above mission list is out of order. It should be as follows:
1. Save Waylon McCrane from the Tuatha
2. Investigate the mysterious occurrence (i.e. rescue the Tuatha)
3. Repel the Fir Bolg from the Misty Wood
4. Find out what the Red Caps are up to
5. Stop the eternal battle
You can play the first mission at level 27, but the rest won't be assigned to you until you hit level 30.
