I Put a Spell on You

 is a side quest in Fallout: New Vegas. Camp McCarran has been compromised and the agent is feeding information to Caesar's Legion about NCR troop movements.

Quick walkthrough (NCR)

 * Travel to Camp McCarran and speak to James Hsu or complete The Finger of Suspicion.
 * Speak to Captain Curtis and then to Carrie Boyd. IMPORTANT: Do not inform Curtis about that lead, this will make the quest impossible to finish!
 * Once you've got adequate information, head to the entrance of the control tower.
 * Between midnight and 1:40 a.m., the spy will wander over calmly (armed with a 9mm pistol).
 * If you're asked about what are you doing outside so late at night Do not say you're investigating the tower.
 * Remove the disarming codes from the spy.
 * Do not head to James Hsu and report the incident to him as this will cause the bomb to detonate upon leaving the terminal building either via entering the monorail station or leaving for the airfield.
 * Head upstairs, directly over Hsu's room, and run for the monorail.
 * Defuse the bomb.
 * Now report to Hsu.

Detailed walkthrough (NCR)
(In order to complete this mission properly, and being able to also complete No, Not Much)

At some point, you will be asked to speak with Captain Ronald Curtis, who is located on the first floor of the Camp McCarran Terminal building to the west of the escalators. He will then ask you to speak to Carrie Boyd and Contreras. Talk to Boyd, and then ask her about break-ins. She will say that there have been break-ins at the control tower every night. Ask her for an access key. IMPORTANT: Do not inform Curtis about that lead, this will make the quest impossible to finish!

Go out to the control tower. The most direct route is to go out the back door between the escalators on the ground floor. Move back by one of the planes closest to the wall by the tail rudder and Wait until about 12:30 a.m. You may want to save the game prior to doing the Wait.

Sometime at about 12:55 a.m., Curtis can be seen walking towards the tower. It is very important that you remain hidden; otherwise he will confront you and ask why you're there. If you end the dialog successfully, he will then walk back into the base and you will need to wait until the next day. If Curtis starts shooting at you, run outside to the tarmac, then run back to the tower without opening fire on him. Enter the tower and exit, Curtis will no longer be aggressive. It's possible that Curtis may not appear on the tarmac and will already be inside the tower. If you don't see him by 3 a.m., enter the tower and stay hidden as per the next instructions.

If Curtis doesn't see you, he will walk into the tower. Follow him inside, and stay hidden at the bottom of the stairs while you listen to him talking on the radio. The quest will update and tell you to disarm the monorail. If you have a high explosives skill or high science skill, you can choose to go directly to the monorail. Otherwise, you will have to pickpocket the Activation Code off of Curtis for a loss of karma points.

At this point, DO NOT go talk to James Hsu; If you do, the monorail is doomed no matter what you do. Go back in the first floor door of the Camp McCarran Terminal Building, up the east escalator, and down the hall to the east to the door to the monorail. Walk inside the monorail, and turn left. The bomb will be inside an air vent. Disarm the explosives using 45 Science, or 35 Explosives (skill magazines can be used), or the codes you pickpocketed from the Curtis's pockets.You can also confront and kill him after 'eavesdrop the conversation' is complete for the codes. //This is not entirely true as you can tell Hsu, who asks you to hurry to disarm it, and if you use a turbo before exiting the terminal door to the monorail you will have enough time to get on the monorail to disarm it with your skills or the deactivation code. However, the monorail will still leave and explode, and you will have to go back and tell Hsu that the monorail was destroyed.//

Once the bomb is defused, if you have not already killed Curtis you may wish to return to the control tower and finish him off for the extra experience and his equipment. (Note: You can get the equipment anyways, for Hsu tells you he wants to arrest Curtis. You can loot his body in the tower after speaking to Hsu, but you'll miss is the extra experience.) Return to Hsu, he'll reward you with some caps and a reputation boost. Upon killing Curtis (before reporting to Hsu), the NCR guards on the tarmac may turn hostile one you, so run quickly back to terminal. You should have no problem collecting your reward and xp from Hsu despite the hostile guards outside.

You can also complete the quest and gain the Experience Points with killing Curtis in the tower before hearing the radio conversation (though this is not recommended). When you report it back to Hsu, he will be surprised and tell you Curtis could not be the spy as he was the leader of the investigation. After that, it will be revealed that there's a bomb on the train, the explosion of which you won't be able to prevent. After the train explodes, report it back to Hsu, and then the quest ends, with you gaining nothing but the XP.


 * Alternatively, if you use the response "Hsu wont trust me enough to let me investigate." you can help The Legion to blow up the monorail.

Quick walkthrough (Legion)
Talk to Curtis, and choose the option Hsu won't trust me enough to let me investigate. Go through the speech options until you get the quest to blow up the monorail.
 * If your Reputation is high enough with both the Legion & the NCR you can get the quest from Hsu, then talk to Curtis and you are given a option "I Know who you are, and I work for the Legion too"

Follow the map marker to the garbage bin in front of the ticket counter, and take everything inside it. If you don't take everything, you won't be able to frame Crenshaw.

Once you picked up all the items in the garbage bin, go to Hsu and tell him you will investigate the information leak. Then go to the monorail. If your reputation is high enough you can just walk past the soldiers. If not, then there is a change of guards at 9am and 6pm (please confirm times), which should give you a short time to sneak to the monorail without getting any problems with the guards (Or snipe them while hidden for the extra xp.). Alternatively, don an NCR uniform and the guards will let you pass without attacking. Now enter the monorail, go left, and there is a vent on the wall which you can activate to plant the bomb. The quest tells you to leave the monorail and watch it depart

Next enter the building, stay upstairs and go into the Concourse. Go left and head to a footlocker that your map marker will point to. Put Abraxo Cleaner, Conductor, Fission Battery, Monorail Sabotage Plans and Wonderglue in the footlocker. Take a left and head outside following the map marker to Crenshaw, who you can just kill and then head back inside and tell Hsu that Crenshaw blew up the monorail. The first option telling him about the evidence will reward 100 caps, so will the second option using speech, and both are still repeatable, which is a bug but a nice way to get a repeatable 100 caps if you need them. The third option doesn't give you anything.

Head back to Curtis and tell him he's in the clear for 550 xp and 150 caps.

Bugs

 * sometimes after Crenshaw has been framed, Curtis will stay in the control tower attempting to report in. Talking to him will result in his usual response when you discover him in the tower. A possible fix for this is to sleep in an owned bed for 24 hours. Another possible fix is fast travelling to the entrance of Camp McCarran, which corrects his location.


 * There is a bug when trying to eavesdrop on the conversation causing Victor to appear randomly standing on the steps blocking your way. No conversation is held by the NCR on the radio, thus causing the monorail to explode no matter what you do.


 * After successfully entering and eavesdropping on the spy, leaving the control tower causes any followers to stop following. They will wait in front of the tower until you talk to them and tell them to stop following and then to follow you again.


 * Upon entering the tower, followers get stuck in an endless loop of appearing a few feet above the ground, settling on the ground, and then reappearing back in the air again. Upon exiting, followers will try to follow you but upon hitting some kind of invisible wall will be teleported back to the door. The latter is solved by simply walking away, causing the wall to disappear and allowing followers to continue following normally.


 * It is possible to get the 100 Cap reward for framing Private Crenshaw unlimited times, all that is required to do this is to talk to him and tell him you found out who sabotaged the monorail and provide him with the speech check as evidence. Once you have done this repeat to keep getting the 100 Cap reward. This continues to work even after the quest has been completed.


 * Whilst investigating the late-night break-ins, the game does not allow you to eavesdrop the conversation and the spy will eventually discover you. A possible workaround for this situation is to make a save outside the radio tower after the spy enters it - if you hear the conversation when you go in, the quest can continue normally. However, the conversation will stop every time the spy has to give a reply. There are two ways to fix this. Firstly, you can pause the game every time the spy has to reply to continue the conversation. If this does not work, you must pickpocket one item from him for every reply. It's best to take weightless items, such as his the 2 codes and 9 9mm cases he is carrying, which can be taken with a Stealth skill of 20. Each item you take will result in the conversation advancing.


 * There's a bug which prevents you from saving the monorail - even if you get on the monorail and disarm the bomb, the monorail still blows up (still unfixed even with the latest patches for all consoles). Hence, if the player wishes to access The Strip easily through the monorail, they should do so before initiating this quest OR before the portion of the quest where the player has to save the monorail. However, this bug can be avoided if the player simply kills Curtis, loots the deactivation codes from his corpse, and ignores the "go inform Hsu" objective, instead heading straight to the monorail. Once there, you can deactivate the bomb without any complications and can proceed with the quest as normal.


 * There is a chance that when you are waiting for Curtis to enter the tower, he will simply walk in and out of the McCarran Terminal Bulding every second from 12am to 2am. If this happens, you will have to load a save from an earlier point in the quest, such as before receiving the lead from Carrie Boyd. If you don't have a previous save, PC users can type "resetquest 000e790f" in the console, erasing the quest. To restart the quest, you will have to speak to Hsu again. An alternative workaround is to crouch down and shoot at Curtis when he exits the building. If done correctly, he will begin to follow you, lead him to the tower and wait in front of the door till hes just about in conversation range. Go inside the tower and watch the compass. When he's right outside the door your companion's indicators and your companions will start to blink. Exit the tower and you will immediately be forced a dialogue with Curtis. Work through the conversation and when done he will enter the tower. Follow behind him and the quest will continue as normal, allowing you to eavesdrop on the conversation.


 * If you end this quest without saving the monorail, Hsu will not grant you the reinforcements for Bitter Springs, thus making the Quest No, Not Much unsolvable. However, reaching 'Liked' status with the NCR allows Hsu to send the reinforcements before completing this Quest.


 * If you quicksave just before Curtis enters the tower and then reload, Curtis remains standing exactly where he was when you saved, but is invisible and will not respond to either speech or pickpocket attempts. A partial fix is to head back into the terminal building and wait till daylight hours. Curtis will reappear and you can now interact with him, but he will remain in position, thus never heading into the tower and making the quest unsolvable.


 * If you decide to leave the tower when you're supposed to listen to the conversation and fast-travel to another location, after ~3 hours Curtis will appear and ask you what you are doing there (in another language with normal subtitles). If you end the conversation well, he will travel back to the camp. However, you will not be able to listen to the conversation after this.


 * If you're on bad terms with the NCR and initiate this quest as a Caesar's Legion supporter, then get on good terms and speak to the Colonel about completing the quest for the NCR. The explosives in the trash can become non-existent and the Control Tower becomes vacant.


 * Sometimes no matter what time or day you're there, the spy will never show up. A possible solution is to reload an earlier save.


 * If Boyd got locked in the interrogation room during The Silent Treatment, you will be unable to speak to her to complete this quest.


 * If Curtis starts a gun fight with you in the tower, 10 of Spades may suddenly appear out of nowhere.


 * Sometimes the game will bug and not allow you to open the garbage can in front of the ticketing counter, thus rendering the quest impossible to complete.


 * If you need Col. James Hsu to send troops to Bitter Springs for the quest "No, Not Much", when you get to the monorail part, get into the monorail and defuse the bomb. Then, while still in the monorail, quick travel to Fort McCarran. You should be able to go straight back to Col. James Hsu and ask him to send troops to Bitter Springs, and he'll say yes. If you go back to the monorail, it'll depart and explode. This a small workaround if you need to get the "No, Not Much" quest completed without the monorail blowing up.


 * Activating the Pip-boy at the monorail may cause the game to freeze.


 * After defusing the monorail bomb and reporting Curtis as the spy to Hsu, returning to the monorail results in NCR personnel becoming hostile.


 * After discovering the break-ins in the control tower you have the option to inform Curtis about it. If you do this the quest will glitch, Curtis will enter the tower as normal but you'll never hear the radio conversation, preventing the quest to be completed. Note: Confirmed on PS3 but it's doubtful that this is a bug. Informing the culprit that you know would most likely cause the quest to go this way. The quest can still be continued by confronting Curtis in the tower.


 * Using The Console Clicking On Curtis And Typing Enable will make the radio say the first sentence you will have to Type Enable Every time a sentence ends to hear the entire conversation.


 * There is a chance that the explosives will not be in the trash can by the ticket counter.


 * You may not be able to communicate with Boyd to continue the quest if you kill Silus when you first enter the interrogation room. Specifically, this happens when you successfully convince Silus you are working for Ceasar through a series of Intelligence checks and then continue to attack him after Boyd asks you to leave the room while Silus is no longer aggressive. It appears Lt. Boyd is no longer able open any dialog with the player after this. This can be fixed by resurrecting Silus through the Console and speaking to him again (you might need to use the Console to unlock the interrogation room door). If your Speech is over 50 you should get a dialogue option to threaten to beat him up. If you select that option Silus will turn hostile but will not attack you; simply kill him again and leave the interrogation room. Boyd should be outside and you can talk to her again.


 * You may not be able to enter the Monorail because of a invisible wall glitch before you inform Hsu, to prevent this problem you need to inform Hsu that you killed Curtis and then proceed to the monorail as fast as you can, however there is a good chance you won't get there in time, thus causing you to fail the Quest.


 * If you help the Legion blow up the monorail but do not have a high enough Speech or reputation level with the NCR for them to help you, you have to go back to Curtis and say "Hsu won't let me help". Curtis then tells you to rig the monorail to explode regardless. However, a glitch may mean that you can't plant the bomb, making the quest impossible to complete. The monorail can still be used to travel to The Strip.


 * If you kill Curtis and then report to Hsu, choosing the 'You won't have to worry about intelligence leaks' dialogue option will render the quest impossible to complete; upon defusing the monorail bomb, the monorail acts as though it detonated and can not be used to access The Strip. Upon returning to Hsu, there are no further dialogue options available. The only fix for this problem is to reload an earlier save.


 * After you start the quest make sure to get the key to the control room from Boyd before starting the interrogation, interrogating Silus and kill killing him will make Boyd impossible to talk or pick-pocketable. Making this quest impossible because she gives you the key to the control room.

Fixes
If you've killed the spy and already spoken to Hsu about it, but don't want the monorail to blow up, you can follow the steps here to create a mini-mod which would allow you to stop the explosion and complete the quest (not working to everyone, although following these instructions, it may work).

If you don't want the monorail to blow up on the Xbox 360 version, avoid the event trigger. This trick works by jumping up onto the guard rail right next to the train and fallowing it into the train car.