The Circle of the Black Thorn was a powerful secret society, whose members were considered to be the instruments of the Senior Partners on earth. Their goal was to enforce Wolfram & Hart’s apocalypse plans in return for power. The Circle’s members were composed of Archduke Sebassis, Senator Helen Brucker, Cyvus Vail, Ed, Grand Potentate of the Fell Brethren, the leader of the Sahrvin Clan, and Izzerial “the Devil”.
Through a vision given to him by Cordelia, Angel discovered that the Circle was the way to destroy W&H’s evil plans. Without consulting his friends, Angel pretended to become corrupted by the evil law firm. He infiltrated the society and ‘proved’ his loyalty to them by pretending to be the true power responsible for the resurrection of Illyria. He also aided several Circle members using his law firm; sacrificed Drogyn; and signed away his right to the Shanshu Prophecy.
After confiding in his friends, Angel and his crew set out on a mission to wipe out the Black Thorns as an indirect attack on the Senior Partners. They would never be able to stop the Partners, but wanted to show them that that they would never be controlled. Angel secretly poisoned the key player of the Black Thorns, Archduke Sebassis. Izzerial and the three other unnamed human members were slaughtered by Illyria. The leaders of the Sahrvin Clan were slain by Lindsey with the aid of Lorne. Spike wiped out the Fell Brethren and their Grand Potentate, Ed.