Rescue Sinthia

Save Sinthia is a side quest in Fallout.

Quick walkthrough
If the Vault Dweller spends a night in the Crash House Hotel in Junktown, they will 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.

Detailed walkthrough
There are three ways to solve this quest:

Peaceful solution
As soon as the raider can see the Vault Dweller, he will enter dialogue. When talking with the raider, the Vault Dweller must assure him that no one is going to hurt him in order to have him believe that the Vault Dweller is his friend, and not an enemy. If the Vault Dweller's Speech skill is high enough, he/she can convince the raider to leave without a fight. If it is not high enough, they may need to pay either 100 or 200 caps, depending on what dialogue options are chosen.

Violent method
Another option is to talk 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 while he is pondering. He will attack the Vault Dweller instead of Sinthia, allowing the him to kill the bad guy and save the prostitute.

Sneaky way
Again, like the option above, the Vault Dweller should talk to the raider in a calming manner. When the raider says he needs to think about it, the Vault Dweller should activate the Sneak skill. If it is high enough, Both the Vault Dweller and Sinthia will be able to sneak behind the raider without him reacting. Shooting him will knock him unconscious. At first, Sinthia will think the raider is dead, but the game confirms he is not.

Rewards

 * 1000 or 400 XP.
 * A free night at the Crash House.
 * Sinthia's "services".