The summoning of Frostlord Ahune requires a series of quests available during the Midsummer Fire Festival.  On the Horde side, the quests starts with the Earthen Ring Elder (female troll) located at the Midsummer Fire Festival area just north of the Flightmaster in Shattrath City.

Your first quest with her is titled: Unusual Activity.

You are sent to Zoram Strand, in the western coast of Ashenvale to kill some Twilight’s Hammer Cultists to retrieve a Twilight Correspondence in order to unveil their dark plans.

The image below shows you in the mini-map where in the Zoram Strand to find the ruins at which the Twilight are camping at.  These are level 21 mobs. Unless the letter item that drops is random, mine at least dropped from the mob by the blueish bonfire. Once you loot the letter—do not teleport/hearth out. Open your inventory (bag). You will find a totem item given to you by the Earthen Ring Elder.  Click the totem.

Below you can read the text within the Twilight Correspondence. It unveils the dark plans of the Twilight’s Hammer in alliance with the Neptulon-sworn heretic naga faction.