Whilst the player is in Candlekeep in Chapter 6, Scar is attacked and murdered by two doppelgangers. One of the doppelganger then took the shape of Scar and attacked Duke Eltan. Though the duke overcame the attack, he did receive injuries and to make things worse, his healer, Rashad was actually a doppelganger whose 'cures' only made the Duke's health worse.
The player first meets Scar in Chapter 5 on the Wyrm's Crossing when he asks the player if he/she would investigate the mysteries at the Seven Suns. If the player fully completes that mission, Scar would be informed that the Seven Suns has been infested with doppelgangers and that his friend Jhasso is alive and well.
Scar then wants the player to investigate the disappearances of random people in Eastern Baldur's Gate. If that mission is successful the player will have killed an ogre mage and retrieved a ruby ring. After the second mission, Scar introduces the player and their party to Duke Eltan, who then gives the party their third and final mission in the fifth chapter.