At The Hellmouth
In 1937, the Order settles in Sunnydale in an attempt to bring about the end of the world. In preparation for the opening of the Hellmouth, the Aurelians are responsible for a series of gruesome murders. The murders cease after an earthquake interrupts the ritual that the Master is performing to open the Hellmouth, leaving the Master severely weakened and trapped within the portal he had been trying to open. The Order then lies low until early 1997.
In 1997 the time for The Harvest arrives. During the night of the Harvest, the Master plans to obtain strength from the blood of the victims of one of his minions, the so-called Vessel, through a mystical link between the two. The Master hopes to gain enough strength to break through his prison, and thereby open the portal that had trapped him in 1937. However, the Harvest is ruined by the interference of the Slayer, Buffy Summers.
Weeks later, some Brethren of the Order bring about the prophesied rise of the Anointed One. The Aurelians also decoy Buffy away from the true Anointed One by making a vampire of the maniacal Andrew Vorba, who is in turn slain by Buffy. Meanwhile the true Anointed, a child named Collin, is taken to the Master's presence.
Due to the actions of Buffy, the Order's numbers continue to thin, and many of the Master's most appreciated acolytes end up as dust. Dispirited, the Master summons the Three, a trio of battle-scarred vampire warriors, to hunt down the Slayer. They fail, thanks to the intervention of Angel, and lay down their lives in penance; The Master comforts himself by allowing Darla to kill them.
By May 1997, a number of portents announcing a new Apocalypse prompt the Aurelian vampires to once again perform a number of murders in preparation for the liberation of the Master and the fulfillment of the prophecy in the Pergamum Codex: the Slayer's death. The Order sires a large number of vampires to serve as the Master's army. The ancient vampire succeeds in escaping his prison, which causes the "opening of the Hellmouth": a portal to the Old Ones' universe opens and from it emerges a demon commonly referred to as the Hellmouth Spawn. Buffy finally slays the Master as Rupert Giles and others fight the Hellmouth demon back, averting the end of the world. A number of other vampires are also slain and many flee.
With the Master gone, the Anointed One remains as the leader of the Order of Aurelius.
Read more about this topic: Order Of Aurelius