After a vision from Cordelia Chase pointed him to the Circle of the Black Thorn, Angel used Fred's death and a fake turn to evil to join the Circle and learn who its members were. Angel successfully infiltrated the Circle thanks to his actions and learned that the members consisted of Archduke Sebassis, Senator Helen Brucker, Ed of the Fell Brethren who acted as their representative, the leader of the Sahrvin Clan of demons, Izzerial the Devil, three human members and Cyvus Vail. After Angel had his friends spend the day however they wanted--instructing them to "live the day like it's your last... because it probably is"--, he sent his team (including Lindsey and Illyria) after the members of the Circle.
Spike and the Fell Brethren
Angel sent Spike alone after the Fell Brethren with the orders to "return the baby to its mother and dismember the foster family" which Spike happily accepted. Spike rescued the infant after infiltrating the Brethren and seemingly slaughtered them with ease, before returning the baby to its mother and heading off to meet up with the others.
As Izzerial and the three human members of the Circle left a restaurant, Illyria attacked them in their car. What exactly happened was not made clear, but she apparently slaughtered them messily and left behind only a bloodstained and destroyed car (She had promised Angel to "make trophies of their spines").
Charles Gunn and Senator Helen Brucker
Angel sent Gunn after Senator Brucker, whom Gunn had a prior disagreement with, and also so Gunn could dust her vampire minions as he had been looking to kill some vampires after having dusted very little over the past year. Gunn attacked Brucker and her minions in her campaign office and killed Brucker by throwing an axe into her head, but was left surrounded by her vampire minions. Gunn apparently prevailed in the fight, but was left seriously wounded.
Wesley attacked Cyvus Vail, getting into his mansion by pretending to want to lead a coup against Angel. Wesley tried to kill Vail with magical fireballs, but while he was initially successful at blasting Vail as he caught him by surprise, Vail proved too powerful for him and defeated him. Wesley tried to stab Vail instead, but failed and Vail stabbed Wesley, mortally wounding him. Wesley managed to knock Vail out for a few minutes by detonating another fireball, but was too late to save himself. Illyria showed up, having grown concerned about him, but was unable to help him. Illyria took on the form of Fred to give comfort to Wesley as he died in the form of the woman Wesley loved. Wesley died and Illyria was left enraged. Vail recovered and underestimated Illyria as she was still in the form of Fred and told her to take her "best shot." An enraged Illyria turned back into herself and punched Vail so hard in the head that his head shattered, killing Vail and avenging Wesley.
Lorne and Lindsey versus the Sahrvin Clan
On Angel's orders, Lorne and Lindsey worked together to slaughter the Sahrvins. Lindsey proved to be an expert swordsman and easily killed them with Lorne apparently adding in a high note to disable the demons to help Lindsey. Afterward, Lorne carried out his true orders and killed Lindsey with a silenced pistol on Angel's orders as Angel knew Lindsey would never change. After killing Lindsey, a disgusted Lorne left the Sahrvin bar and Team Angel.
Assasination of Archduke Sebassis
Angel told everyone including Harmony that he was going after Sebassis as Sebassis was the most powerful of the Circle, but this was false information in order to get Hamilton alone, having concluded that Hamilton was the one he should really be concerned with defeating. In truth, Angel used a ring containing poison to poison the slave Sebassis drank the blood of during the last Circle meeting, poisoning Sebassis later on. Sebassis realized too late that his drink was poisoned, and by that time his slave was dead and Sebassis soon followed, dying of the poisoned blood.
Having received word of Angel's betrayal and plans to go after Sebassis from Harmony, Hamilton confronts Angel in a fight at Wolfram and Hart. Angel admits to already killing Sebassis and luring Hamilton into a trap so they could fight one on one. Unfortunately, Hamilton proves too strong and too powerful for Angel to even hurt and beats him down. As Hamilton gets ready to stake Angel, Connor joins the fight and knocks Hamilton out for a moment, having realized something was wrong due to Angel's earlier visit with him. Angel and Connor fight Hamilton together, but even their combined strength is no match for Hamilton's and Connor is knocked out. Hamilton ends up bragging that the source of his power is in his blood and Angel takes advantage of that, drinking from Hamilton for a moment. Hamilton throws him off quickly, but that small drink causes Angel to gain Hamilton's level of strength and the two are more evenly matched. Finally Angel beats Hamilton down and punches him so hard in the head, his neck breaks, killing Hamilton.
Angered by the destruction of the Circle and the death of Hamilton, the Senior Partners destroyed the Wolfram and Hart building and sent an army after the surviving members of Team Angel. Eve apparently died in the collapse of Wolfram and Hart, staying behind as she had nowhere else to go and Angel sent Connor home. These events ended up leading to the Fall of Los Angeles.