Kill 20 Plagued Hatchlings, then return to Betina Bigglezink at the Light's Hope Chapel.
The Argent Dawn recently learned that the Scourge are creating their own plagued dragonflight! We must stop them -- if the Scourge gain a force of dragons they'll sweep across Azeroth unchecked!
Their necromancers are breeding plagued dragons at the Scholomance, in the middle of Darrowmere Lake.
Go to the Scholomance and kill as many hatchlings as you can... before they get any bigger!