The mission will begin after completing "The Great General".
Head to Rathir and speak to Elunda Carth in Upper City M8(27).
The man won't agree to send his army, but will lend you a group of refugees that are willing to fight. Additionally, if you succeed in persuasion, he will give you an epic ring increasing the damage you deal and gold dropped by the enemies.
You can now go to the docks and take the ship to Mel Senshir. The further description can be found in the section of the guide dedicated to the land of Klurikon.