Kings' Gambit

Kings' Gambit is a quest in Fallout: New Vegas.

Objective
Kill Pacer in a way that implicates someone other than the NCR, or talk to The King into ceasing hostilities with the NCR.

Detailed Walkthrough
Once you have completed the quest Things That Go Boom, speak to Ambassador Crocker, who will assign. Crocker tells you about all the violence in Freeside being caused by The Kings. He gives you two options: either kill Pacer (the main source of the violence) or solve the problem diplomatically.

Option: Kill Pacer
If you have already talked to the ghoul Rotface in Freeside, he may have given you tips, two of which include the fact that Pacer has a heart problem and too many drugs will kill him and another is he has a feud with the Van Graff family. This will add two optional objectives to the quest, one to kill Pacer by adding Psycho to his Jet and one to kill Pacer in a way that implicates the Van Graff family.

Method: Frame the Van Graff family (Jean-Baptiste Cutting's note)

 * 1) Examine Pacer's stash of Jet, then return to the person who gave you the quest
 * 2) Talk to Ralph at Mick and Ralph's and ask him to forge a handwritten note written to Pacer from Jean-Baptiste Cutting.
 * 3) Go to Pacer's room (first room on the left, third floor of The King's School of Impersonation).
 * 4) Replace Pacer's stash of Jet with the handwritten note.
 * 5) When Pacer checks his stash, he will immediately run over to the Silver Rush and get himself killed.

This method works even if you killed everyone in the Silver Rush building earlier. Just follow Pacer there after planting the note in his room and kill him yourself with a plasma or laser weapon to frame Van Graffs.

Method: Frame the Van Graff family (plasma grenade)

 * 1) Go to Pacer's room (first room on the left, third floor of The King's School of Impersonation).
 * 2) Wait for Pacer to appear. If your sneak skill is low, wait for him to fall asleep.
 * 3) Reverse-pickpocket a plasma grenade onto him.
 * 4) Sneak out of the building.

NOTE: All of the Kings members attack you, on all floors if you select this option. (Same thing as happens if you sneak-kill Pacer with a silenced weapon. Somehow, the Kings instantly know you killed him anyway, and all go hostile.)

Method: Spike the Jet with Psycho (Requires 60 Medicine and 1 Psycho)

 * 1) Go to Pacer's room (the first room to the left on the third floor of The Kings' School of Impersonation)
 * 2) Add the Psycho to the stash of Jet under his bed. The stash appears to be a carton of cigarettes.
 * 3) Pacer will die immediately when he checks his stash.

Method: Just kill Pacer
You will fail the quest and lose a substantial amount of fame with Freeside, however you do get a reward (if you apologize) are still allowed to move onto the next quest.If you wish to easily regain or fame with Freeside, go the Atomic Wrangler and talk to James Garret. You will have to pay more caps depending on how infamous you are.

Option: Solve diplomatically
If you haven't used your favor from G.I. Blues yet, you can use it to ask The King to stop the violence and turn the quest in. However, if you have already used it, the King will say no and you will have to return to Ambassador Crocker and tell him that the King will not stop the violence. Crocker will then give you two options (on top of the option to kill Pacer): Talk to Colonel Moore at the Hoover Dam or talk to Colonel Hsu at Camp McCarran.

Method: Colonel Moore

 * 1) Head to Hoover Dam and talk to Colonel Moore, she will tell you to tell the Kings to stand down or be destroyed and offers to send a squad to back you up.
 * 2) Anything you say to the King will cause him to refuse and a fight will break out, and you will fail the mission when you tell Crocker what happened. However you will not gain any Freeside infamy if you let the troopers do all the shooting, and you can get the King's unique suit and you even get a reward of 300 caps from Crocker if you apologize and you get to move onto the next quest.

Method: Colonel Hsu

 * 1) Go to Colonel Hsu at Camp McCarran and tell him about the situation in Freeside and he will tell you to offer the King support from the NCR.
 * 2) When you get back to the King and tell him the NCR have offered their support (if you are rude to him, his gang will open fire and you will fail the quest, although you will not gain any Freeside infamy if you let the troopers do all the shooting, and you can get the King's unique suit and you even get a reward of 300 caps from Crocker if you apologize and you get to move onto the next quest.)
 * 3) When the King agrees, Pacer will not agree with the deal and will instead start shooting the troopers. Help kill Pacer or just let the troopers finish him off and head back to Crocker.

Reward
The player will be rewarded with 1500 XP, 300 caps(600 if resolved diplomatically) and NCR fame. In addition, the quest For the Republic, Part 2 will begin.

Bugs
Possible bug fix: Though it might be no bug, try after discovering the stash (and king saying 'no' to request) talking to the ambassador first. With a medicine skill of 60 or higher you can suggest to poison the jet and after that there is an option to actually do that within the dialog.
 * Ambassador Crocker may not give you a reward when you complete the quest, yet will oddly give you a 300 cap reward when you fail it and apologize.
 * When attempting to lace the stash with Psycho, the dialog won't allow it, saying "You could lace it...if only you had some Psycho" despite having numerous Pychos in inventory.
 * No Jet stash under Pacer's bed (you must get the rumor tidbit from Rotface for the stash of Jet to spawn.) On the Xbox 360 sometimes whether or not you get the rumor tidbit the stash still doesn't appear under his bed. Possible bug fix: Type the following into the console: prid 001205BC enable This should cause the stash of Jet to spawn under Pacer's bed.
 * After telling Crocker that the King won't stop the violence, you can still request that the King do so as a favor but it will not accomplish anything in regards to the quest.