After learning that the raiders are attacking Vault City, the Chosen One is being tasked to find out where they are and kill them. One can directly go to them (near the direction from Vault City to Broken Hills). After that, they must go into the cave. Be aware of traps, like explosives or holes (they lead to bottom level where the radscorpions are). Go to the eastern parts, where there are more traps, but also two fenced doors which are locked (a very high Lockpick skill is required to open). The alternative is to study the map in Bishop's safe, then go there, and be transported to the back entrance, earning 500 XP. Then the Chosen One must kill all mercenaries which can be quite tough, given the equipment they possess. After that, collect the dogtags from Angel-Eyes, Tuco and Blondie to open the safe. Inside is some treasure, along with a logbook which must be shown to Joanne Lynette in Vault City.
If both the account book and Bishop's holodisk are given to Lynette within one conversation, the 1000 XP for the account book will not be rewarded. This can be prevented by dropping the holodisk on the ground, giving the account book to Lynette, picking up the holodisk, and only then giving the holodisk to Lynette.[verified]