Silus Treatment

 is an unmarked quest in Fallout: New Vegas.

Quick walkthrough

 * Travel to Camp McCarran and enter the terminal.
 * Go to the west end of the second floor. Find Carrie Boyd in a room to the north.
 * Speak to Carrie Boyd and agree to help her interrogate the prisoner. (You cannot get the dialogue to help her if you are wearing NCR faction armor.)
 * Interrogate the prisoner and get him to tell you about Caesar and the spy at the camp.

Detailed walkthrough
Silus is held captive in Camp McCarran, and the NCR is attempting to interrogate him. He will not give information to the NCR, and interrogator Carrie Boyd is looking for help. She informs the player that the NCR does not allow torture of prisoners. The player can suggest a truth serum, beating the prisoner, or calling him names.

If the player has a high enough reputation with the NCR, Lieutenant Boyd will allow the player to go in and speak with the Centurion. The player will go in unarmed, unless the player's sneak skill is high enough to bring in holdout weapons.

The Courier can either break Silus or help Silus escape.

Break Silus
The Courier can speak with Silus or attack him outright. Here, a relative knowledge of Latin will help you understand the dialogue choices:
 * Should the player speak with Silus:
 * Passing a speech check will result in the legionary attacking. After a brief fight, Lt. Boyd will come in again and ask Silus if he wants more. When the legionary refuses, the player will briefly speak to him again, and begin attacking once more. After a second round of fighting, Silus will talk.
 * Passing a series of speech checks with high speech (90 is certainly enough, though the required Speech skill is not shown) results in him giving the intelligence you need, similar to the method using intelligence detailed below.
 * With an intelligence of 8 or higher, the player can persuade him into thinking that you are working with the Legion and are here to assassinate him; this will result in him telling you all of his plans.
 * "Timeo Danaos et dona ferentis." means "I fear the Greeks, even when bearing gifts"; this is a line from the Roman poet-historian Virgil, a reference frequently evoked in the context of the Horse of Troy (mistranslated as "Beware Greeks bearing gifts".
 * "Corruptio optimi pessima." means "Corruption of the best is the worst possibility."
 * "Legum servi sumus." means "We are all slaves to the law."

You can also kill Silus to gain history points with Boone. Just take Boone with you an give him a weapon like a knife. Enter the room, go through the speech checks, exit the room and talk to Boyd to get your reward. Take the weapon from Boone and kill Silus. Talk to Boone to advance your history with him and give him back the weapon and leave.

After the information is gained from Silus, you can no longer interact with him, and Lieutenant Boyd will pay you for your troubles.

Help Silus escape
If the player has already been invited to Ceasar's camp at The Fort, they have the option to tell Silus. The player can choose to stage a fight with him and retrieve his silenced .22 pistol from the locker in the next room. When the player returns for the second round of interrogation, Boyd will confiscate all weapons except the pistol. After giving Silus the weapon, he will fake being unconscious. Boyd will come back in and say it looks like he is "all tuckered out", and she and the player will leave. On the way out, she will tell the corporal to go clean Silus up and he will go in and tell Silus to get up. Silus will kill the Corporal and dress in his clothes. He will then sneak out undetected by the NCR. The player will not lose any reputation with the NCR as a result.

Note: After Silus is dressed as an NCR corporal he will not speak to the player while he leaves.

Rewards

 * NCR Fame
 * Caps (varies depending on resolution method)
 * XP (varies depending on resolution method)

Bugs
Reloading the auto save that occurs when you enter the room, may cause all your weapons to spawn back in your inventory,
 * If you leave the room after the first time you talk to Silus, you can not get back in, and further interaction with Lt. Boyd only result in her saying "Let's talk after we finish this up" and ending the conversation abruptly. There doesn't appear to be any way into the room after this point.
 * While ED-E is a companion, during the phase of the interrogation where Lt. Boyd speaks to Silus and ask if he wants more. ED-E may enter the room and start to attack Silus when he gets aggressive. When the quest is complete and you leave the room, ED-E will still be inside and will not be able to escape. A way to avoid this is to tell him to wait outside before you enter the interrogation room. Rex has also done this.
 * Using the Mysterious Stranger perk can be hazardous, as he can appear in the room while using V.A.T.S and kill Silus outright, forfeiting the NCR rewards.
 * If the player is wearing Boxing gloves (Fallout: New Vegas) before Carrie Boyd takes your weapons from you then they will stay on your fists and remain so for the rest of the game. It grants the same effectiveness as regular unarmed blows and other weapons can still be equipped. This also happens with Bladed gauntlet, Cram Opener, Recompense of the Fallen and apparently other Unarmed weapons.
 * The door has many opportunities to bug - if you save after Boyd enters the room to introduce you (perhaps only as she is starting to walk out?) you will not be able to enter the room to interrogate Silus after she leaves. Also, if you decide you want to pummel Silus to death to earn points with Boone towards triggering his character quest I Forgot to Remember to Forget, Boyd may get stuck in the room afterwards, preventing you from talking to her again and completing I Put a Spell on You. (360)
 * Talking to Boyd without the quest she will tell you that you need to do more "ass kissing" before you can help her. If you talk to Colonel Hsu and get the directive to talk to Boyd about helping her, she will have the same dialog options as before and will not let you help her. ✅

Exploit: Getting all NCR Rewards
If you decide to go with the NCR route, Killing Silus to get the +1 with Boone and to get the Legion Centurion Armor will not allow you to get the payment reward from Boyd, and may cause problems getting to the next step in I Put a Spell on You, if you haven't already completed that quest. However, if you have a stealth boy and an explosive, you can get the +1 to Boone, the Legion Centurion armor that Silus wears, AND get the cash reward from Boyd.

First, make sure you have at least one follower with you, and then place an explosive (A regular stick of dynamite will work) in the follower's inventory. (Boone is recommended, since this exploit primarily exists to get the +1 with him in addition to the other rewards.)

Next, instruct Boone to stay close to you, and enter the interrogation chamber. (SAVE BEFORE YOU DO THIS.)

Move to the far side of the wall, as far away from the door as you possibly can. Boone will enter the room. Make sure you haven't spoken to Silus yet.

Remove the dynamite from Boone's inventory and drop it on the floor. By leaving the stick of dynamite on the floor, instead of keeping it in your inventory, you will able to use the dynamite inside the chamber. This normally isn't possible since your weapons are stripped from you when you enter. (Need confirmation of whether you can sneak explosives inside with a high sneak skill)

Once the dynamite is on the floor, leave it there, and then leave the room. As long as you haven't spoken to Silus yet, the door should be unlocked. Make sure Boone leaves the room with you. You have to get Boone out of the room before the door locks itself, or Boone will be stuck inside. Relocate Boone to a safe distance away from the chamber so that he won't engage Silus if he becomes hostile. If you have any other followers with you, do the same for them.

Next, push Boyd so that she's close to the door. The idea here is that she's immediately within reach to engage in dialogue as you exit the interrogation room, so put her a couple of steps in front of the door, near the vending machine. (You may test her positioning by entering and exiting the room to see if she's within reach.)

Re-enter the room. To recap, you should have:
 * A piece of dynamite on the floor
 * A stealth boy in your inventory
 * Your followers at a safe distance away from the chamber
 * Not yet spoken to Silus
 * Boyd positioned next to the door

If you have completed all five of these checkpoints, make a new save file.

Now you can proceed to interrogate Silus. The standard "beating" approach is the most effective for this. After the first time Boyd comes in to talk, she will harass Silus, and then walk out again. If Boyd moves away from her specified location during this part, leave the chamber and push her back. It is critical that she remains there. (In fact, it might be pointless to bother positioning her until after she makes her interruption and leaves, so you only have to do it once.) Next, walk up to Silus and continue beating him. Don't talk to him, just beat him. Talking to him before beating him at this point will cause Boyd to move AGAIN. (she magically teleports elsewhere.) Continue beating on Silus until he divulges his information about Caesar and the spy. The door should now be unlocked, allowing you to exit. However, DO NOT DO SO.

Look through the window and make sure that Boyd is in the correct spot. If she is not, revert to a prior save. If she is, push Silus until he is literally bumping up against the window. Grab the dynamite that has been laying on the floor this whole time, enter sneak mode, and make one last save file. Reverse-pickpocket the dynamite into Silus' pocket, and immediately run out of the room and talk to Boyd, BEFORE THE DYNAMITE DETONATES. (You will only have about a second or two to do this, you have to be quick.) She will give you the cash reward for completing the quest. End your conversation with Boyd, and the dynamite will now explode, killing Silus. If you positioned Silus correctly, you should be able to loot his corpse THROUGH THE WINDOW, even though you are outside. (You may have to abuse the third-person camera view to do this.)

At this point you should have:
 * The cash reward.
 * The next step in the I Put a Spell on You quest. (That is, if you haven't already completed that quest. I personally completed it BEFORE I did the interrogation, so this needs confirmation.)
 * The Centurion armor.
 * +1 to Boone's history points.
 * A boost to your NCR fame
 * A small amount of Negative Karma for Reverse-Pickpocketing the dynamite onto Silus

Killing Silus normally only gives the +1 to Boone and the Centurion Armor, and at the same time, gives you a PENALTY to your NCR Fame, as well as denying you the cash bonus. If you get the information from Silus before you kill him, you may or may not get the NCR Fame penalty and the next step for I Put a Spell on You. If you kill Silus after getting the information, Boyd's dialogue options concerning Silus disappear completely, meaning you likely won't get the next step in the quest, if Boyd is the one who gives it to you. (This needs confirmation.)