Hello, <name>. It looks like you four have had time to become well-acquainted.
I have my first assignment for you. Kalaran, an ancient black dragon of considerable power, has joined in the hunt for the egg we are protecting. We need to stop him before he gets too close.
Alliance
You will find him and his minions at the Dustbowl, north of Dragon's Mouth. Hunt him down and defeat him. You will likely need the help of your new dwarven allies.
Horde
You will find him and his minions at the Dustbowl, east of New Kargath. Hunt him down and defeat him. You will likely need the help of your new mercenary allies.
Completion
One less dragon to worry about, one step closer to redemption. Onward, my soldiers!
Notes
Upon completing the three previous quests, Rhea speaks telepathically, offering this new quest. Remember that the vikings merely need to get within 40 yards of a hostile unit to attack, so don't go crazy. Darkflight Soldiers are level 46 drakonids with 2388 health. Kalaran is a level 47 elite fully-grown black dragon with 9950 health. Use the vikings' abilites--they can take care of Kalaran if Olaf stays on top of the aggro list. The quest completes automatically once all five hostiles are killed.