Wildlord Antelarion has implored you to travel to Death's Door. Once you arrive there, use the Druid Signal to call down an Evergrove Druid so that you can speak with them.
Now there is an even greater threat from the Burning Legion. To the south is a portal known as Death's Door, which opens upon the horrific world where the Legion breeds its deadly hounds.
To get there, exit Evergrove by heading east up the ramp. Follow the path south, through the Bladed Gulch, Razaan's Landing, Razor Ridge and the Scalewing Shelf. Then, take the ramp down into the Vekhaar Stand and enter Death's Door through the tunnel, south of Mok'Nathal.
Once there, use this druid signal.