Lets' talk this over... gun to gun
If the Vault Dweller spends a night in the Crash House Hotel in Junktown, they'll wake up to find the hooker Sinthia held hostage by a random raider in the room adjacent to theirs. Marcelles will beg the Vault Dweller to defuse the situation.
There are three ways to solve this quest:
As soon as the raider can see the player, he will start dialogue. When talking with the raider, the Vault Dweller ought to assure him that no one's going to hurt him, and to have him believe that you're his friend and not an enemy. If their Speech skill is high enough, they can convince him to leave without a fight, but if it isn't high enough they may need to pay him either 100 or 200 bottle caps, depending on what they say and when.
Another solution is to begin talking with the crazed raider in a calming manner. If he says he needs to think about it, the Vault Dweller should walk in on him. He will attack them instead of Sinthia, allowing the Vault Dweller to kill him and save the prostitute.
Again, like the option above, the Vault Dweller should talk to him in a calming manner. When the raider says he needs to think about it, the Vault Dweller should activate the Sneak skill. If it's high enough, they'll be able to sneak behind him without him reacting. Shooting him will knock him unconscious. At first, Sinthia will think he's dead, but the game confirms he's not.
- Sinthia won't sell her services to the Vault Dweller if the raider is killed. Note that if a companion happens to kill him, the Vault Dweller will still be able to do "business" with her.
- If the Vault Dweller doesn't save her, she suffers a gruesome death, causing resentment among the rest of the girls.
- If the Vault Dweller does save her, her "services" will be available (only 40 caps, yet it's for only 10 minutes).