After the coup against Empress Jessamine Hiram Burrows, now Lord Regent, entrusts Jessamine's kidnapped daughter Emily to the Pendleton twins to keep her safe until he plans to reveal her to the public. They also sell their votes in Parliament to Burrows, functioning as a loyal voting block.
Born as conjoned twins in the Month of Darkness, Morgan and Custis entered the world connected by the hands. Although they were seperated, they shared a strong psychological bond for their whole life. According to Treavor Pendleton's memoirs, Morgan is bigger than Custis by "a slight bit".
During their childhood the twins bullied their younger brother Treavor severely. On one occasion they tied him to his crib and left him to the mercy of a"bundle of vipers that they placed next to him. Treavor nearly died of it but the twins were not punished by their father. During their teenage years, the Pendleton clan maintained a familiar relationship with the Boyle family. The brothers had a stepmother who was despised at least by Treavor during their youth who left the family when Treavor was thirteen. This caused their father to sink into a deep depression; it is suspected that Lord Pendleton perished soon after, leaving the family fortune to Custis and Morgan.
Now rich ariostocrats, the Pendleton's used their family's money to live a lavish lifestile, including many visits to the "Golden Cat" bathhouse. At the Cat, Morgan was renowned for his "unusual requests". The Heart given to Corvo by the Outsider also notes that "Morgan takes cruel pleasure in others' discomfort," so it is possible that these requests are sadistic in nature. However, the Pendleton's exquisite lifestyle depleted the family's fortune; coupled with depletion of the Pendleton silver mines forces this the brothers to ask for money from their cousins to be able to visit the Cat.
On one occasion Custis made an "improper remark" to the Empress, and Corvo "ejected him from a state dinner before even asking who he was."
Targeted by Corvo
After the murder of Empress Jessamine, the Lord Regent hands over Jessamines daughter to the Pendletons for safekeeping, knowing that he can rely on the two corrupt aristocrats because he bribes them. The Pendletons furthermore sell their votes in Parliament to Burrows, functioning as a loyal voting block to pass his cruel laws. Through their new position, the Pendletons also got rid of other aristocrats by claiming that they are affected by the plague and then took over their business and fortune. The Heart comments that not all send to the Flooded District by the Pendletons are victims of the Plague.
To prevent the Lord Regent from gaining popularity and more power by presenting himself as the savior of Emily, the Loyalists send Corvo to free Emily and assassinate the twins. Though Morgan's and Custis' cruel treatment of Treavor continued into his adult life (one week before Corvo's arrival at the Hound Pits Pub he was nearly shot by one of them during a hunting trip) it is shown that Treavor still loves his brothers as he tried to convince them to stop backing the Lord Regent and asked their cousins to talk to the twins when his brother stopped talking to him. When this doesn't work, Treavor tasks Corvo with eliminating the brothers who are keeping Emily at the Golden Cat.
After infiltrating the Golden Cat, Corvo finds the bathhouse severely guarded by the City Watch. Both Pendleton brothers are with prostitutes, the room they frequent varies. Their location can be found out by reading the ledger in the madam's bureau or listening to a conversation between the madam and a watchman. Morgan Pendleton will always be in either the Ivory Room or the Steam Room. Custis Pendleton will always be in either the Gold Room or the Smoking Room.
Corvo can eliminate the Pendleton twins with every weapon at his disposal. Also, if Morgan is in the steam room Corvo can use a nearby wheel to increase the steam in the room until the pipe bursts, suffocating both Morgan and the prostitute. This yields an achievement. To get the achievement, Morgan cal also be rendered unconscious and carried into the Steam Room. If Corvo decides to murder Morgan with his sword, a special animation plays. In it he will grab Morgan by the throat, and while Morgan pleads for his life Corvo will slice his throat and drop him on the ground. This animation later reused on Arnold Timsh in The Knife of Dunwall.
Custis can be witnessed expressing his anger toward Lady Boyle, telling his courtesan a bit about his current financial situation. The courtesan will suggest that she dress up as Lady Boyle, and Custis agrees, saying that he would "like to teach her a lesson. As with all other assassination targets, if Corvo decides to kill Custis Pendleton with his sword, a special animation plays. Custis will lunge at Corvo, scratching with his hands, while Corvo holds him by his throat. Corvo will then stab Custis in the side of his neck and drop him on to the ground.
In the non-lethal way of elimination, Corvo strikes a deal with Slackjaw, the leader of the Bottle Street Gang. Corvo breaks into the Golden Cat and interrogates art dealer Bunting on Buntings' safe combination. He then returns to Slackjaw and gives him the combination.
In return, Slackjaw kidnaps the twins, cuts out their tongues, shaves their heads, and puts them to work in one of their own mines.
Returning to the Hound Pits Pub, if Corvo walks toward the tower, he will find Treavor Pendleton. Pendleton says that he never imagined that he would be the one to provide the family's next heir and reveals that he has bastard children. Additionally, he calls for Wallace as he tries to hide his guilt, joking humorlessly and promoting Wallace to "Head Lackey". Although ordering Corvo to kill the twins, Pendleton will be angry at him when he returns. If he finds out that Corvo used the non-lethal elimination, he will leave two gold ingots and a note of gratitude at Corvo's room.