Raiders
Upon returning to Shady Sands, Aradesh will tell you that his daughter, Tandi, has been kidnapped by the Khans (raiders living nearby). Go to their base. Tandi can be freed in several ways: fight the leader one-on-one, simply ransom her for money, or kill all the raiders. Afterwards, return to Shady Sands with Tandi.
By the way, the amount of experience points you earn for this quest depends on which of the three options you choose.
See also:
Fallout 2 Walkthrough: Books in the Game
Fallout 2 Walkthrough: New Reno
Fallout 2 Walkthrough: Modoc