Upon approaching Aelis's Grease summons, he will tell the party to halt and accuse them of being allies of the Cult of the Absolute. Over the course of a rambling speech, he reveals that he was one of the "three finest thieves in Baldur's Gate" alongside Bareki and Sarin before the trio broke into Gortash's office. In doing so, they discovered the secret plot of The Absolute and were hunted down by Absolutists until they fled into the sewers. They became increasingly paranoid until Sarin believed that Aelis and Bareki "had gone strange" and hid the treasure that they had stolen from Gortash. This convinced her friends that she had been taken over by the Absolute so Bareki decapitated her and Aelis burned her until only her skeleton remained.
Throughout the conversation, Aelis will repeatedly address a nearby Grease Elemental as 'his cousin' and pause as if he can hear it speaking. He eventually reveals that he summoned his elementals to bear witness to Sarin's funeral and act as fuel for the fire.
This conversation eventually leads to several dialogue options:
Your paranoia already killed Sarin. Are you so keen to follow her? DC 18 Intimidationcheck
I'm not a cultist. And I don't think your friend was, either. Your paranoia turned you against one another. DC 18 Persuasioncheck
You need witnesses- I'm a witness. Just here to pay my respects. DC 18 Deceptioncheck
Attack
If the check was successfully passed, Aelis will let the party go without a fight and he can no longer be spoken to again. If the check was failed, he will attack.
This is Sarin's final resting place- and a killing ground for all who would disturb her.
„
— Aelis Siryasius
Notes
Aelis's account of what happened to Sarin hints that Bareki has Sarin's Skull. The skull can be retrieved and reunited with her skeleton to help her rest in peace.
DC 18 Intimidation check
Range: 18 m / 60 ft 
AoE: 30 m / 100 ft (Radius) 
Sarin's Skull. The skull can be retrieved and reunited with her skeleton to help her rest in peace.
