Kill Darion

Kill Darion is a side quest in Fallout 2, that requires you to infiltrate the New Khans occupied Vault 15, and kill their leader Darion in order to break their hold on the Vault.

Detailed walkthrough
In order to start the quest you must have completed the Rescue Chrissy quest. After this is done, go to Zeke, the leader of the squatters, who will give you this quest and the red keycard that gives access the elevator to Vault 15.

If you did not kill Phil when rescuing Chrissy, he will be waiting outside the elevator, where he will initiate dialogue and attack. After he is dealt with, you can enter Vault 15 via the elevator.

In order to get to Darion, you will need to pass a few Khan guards. You can kill them or bypass them peacefully with a Speech check. Darion himself is located on the 3rd level of the Vault near the big computer. Upon seeing the Chosen One, Darion will initiate a short bit of dialogue, after which he will alert his bodyguards and guard dog, equip a flamer, and attack you. You only have to kill Darion in the fight that ensues, but his backup can be hard to avoid.

After killing Darion, go to the first floor of the vault. The present Khans are now alerted to your presence, and will attack on sight, and can be hard to sneak past.

Head for the nearest exit of the vault, and return to Zeke.

You will be rewarded with 6000 XP, and will then be able to complete a deal with the NCR.

Bugs

 * Darion and his guards and the rest of the raiders on the 3rd level are considered separate parties by the scripting. Making either hostile will not immediately affect the other (this is logical for raiders->Darion but not the other way round). They will even attack one another if accidentally hit by a member of the other party. This fixes itself upon exiting combat mode.
 * If Darion starts to flee, he can run off into the shower area and disappear. He can be highlighted in VATS by entering the combat mode manually.