The Sargerite Keystone (also referred to as Sargeras' keystone) is a device that can open portals to all demon worlds, including Argus. The ruler of Mardum, Brood Queen Tyranna, was tasked by Sargeras himself with safekeeping it. The Illidari demon hunters were sent to retrieve it for their master but, even though they were successful, they were subsequently captured by the wardens when they returned from Mardum.
The Sargerite Keystone, now in possession of the Wardens, was then held in the Vault of the Betrayer, where the corpse of Illidan Stormrage was stored. Years later during the Third invasion of the Burning Legion, the Illidari and the wardens allied and worked together to retrieve it from the felsworn Cordana Felsong who had stolen it, after which it was brought to the Fel Hammer, the order hall of the Illidari.
Upon Kil'jaeden's death, his Legion ship began to crash toward Argus. Illidan used the Sargerite Keystone to open a rift between Argus and Azeroth, allowing Khadgar to teleport them safely to Azsuna. Argus thus became visible in the skies of Azeroth.
- Patch 7.0.3 (2016-07-19): Added.