Intrigue with Jarlaxle

There's a time limits in this quest. Intrigue with Jarlaxle is a side quest available in chapter 5 in Shadows of Amn campaign.

A Gilded Rope
After the meeting with Matron Ardulace in Ust Natha, Visaj appears on the path just north of Deirex's Tower. He approaches and wants to sell you a Gilded Rope for 1000, if you don't have that much he'll sell just it for 750, if your charisma is 15 or higher, you can talk him down to 500, or you threaten take the rope from him.

Jarlaxle's assignment
Now head down to Deirex's Tower, Deirex the Lich is right there, and you are soon teleported to Jarlaxle's Pocket Dimension. The resident tells you that he wants the gem Deirex processes, he gives you one day to accomplish this before teleporting you back to Deirex's Tower.

Fight with Deirex, who is capable of casting Time Stop, Abi-Dalzim's Horrid Wilting and puts up as a normal lich battle (22,000 XP). Be sure to search his body for the Lich's Tooth and the Jae'llat Wardstone. Also search this place for treasures (some of which are trapped): Take the Jarlaxle's Gems will instantly teleport you back to the pocket dimension. Jarlaxle takes the Gems. Accept his thanks (2500 10,000 XP) or kill (14,000 XP + 12,000 XP). In any case you will be teleported back to the tower.
 * Glitterdust scroll, Wizard Eye scroll, Deafness scroll, Contagion scroll, Remove Magic scroll, Limited Wish scroll, Melf's Minute Meteors scroll, Spook scroll
 * Leather Armor of the Viper +5
 * Jarlaxle's Gems

House cleaning
Go for the lich's treasure (x 3475 y 2730), search the lake for: Leave the tower, go up right to reach the House Jae'llat, his wardstone will open two warded doors and allow you entrance (x 3260, y 1460).
 * Cacofiend scroll, Ruby Ray of Reversal scroll
 * Wand of Frost, Wand of Magic Missiles
 * Spear +3, Two Handed Sword +2, Short Sword +2
 * Crossbow of Affliction +4
 * Ring of Folly (cursed item)

This is, of course, a fairly large battle against many drow warriors and priestesses (each worth 6000 XP), it just wouldn't be a Drow House without those elements, and this is only the first battle, there is another one when you go over to the right, which involves Hindra Jae'llat (14,000 XP) and Istar Jae'llat (16,000 experience). Search the place for treasure:
 * 2500
 * A LOT of Gems (about 50)

Sources & references

 * Baldur's Gate II Walkthrough by Dan Simpson