Spoilers for Wolfheart in the post below.
The Wardens, watchers, jailers, guardians of Night Elf society for 10,000 years, have been through much in the past decade. From once-trusted former members of the Temple of Elune, they took up the supposedly eternal duty of guarding their race's greatest traitor, only to be killed by their own leader for performing the duty appointed to them. The survivors of Tyrande's attack then found themselves buried alive in the crumbling remains of Suramar as it was collapsed by Illidan, their former captive and target of their manhunt.
When Maiev Shadowsong returned from her captivity in Outland as a prisoner of the same Betrayer she and her Wardens had spent millennia holding themselves, she rebuilt the order. This renaissance for the Wardens was short-lived; Maiev's new Watchers were loyal to Maiev first. Despite the results of Maiev's actions and her abrupt departure from Night Elf society, there was still a need for Wardens when the forces of Ragnaros the Firelord made war on Mount Hyjal.
Now the Shadow Wardens, led by Saynna Stormrunner, attempt to make up for Maiev's betrayal and help lead the defense of Hyjal by taking part in the counteroffensive that brings the war to the Firelands' Molten Front. For an organization with so long a history, to be nearly wiped out twice and find your loyalties cast into question rankles. Yet the Wardens endure for one reason: Someone has to be the dagger in the shadows.