Rescue Sinthia

Rescue Sinthia is a side quest in Fallout.

Quick walkthrough
If the Vault Dweller spends a night in the Crash House, a hotel in Junktown, they will wake up to find Sinthia, a prostitute, held hostage by a crazed 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 Vault Dweller is detected by the raider, he will begin dialogue. When talking with the raider, they must assure him that no one is going to hurt him in order to have him believe that they are a friend and not an enemy. If the Vault Dweller's Speech skill is high enough, they can convince the raider to leave without a fight. If the check fails, they may need to pay either 100 or 200 caps, depending on what dialogue options are chosen.

Violent method
If the Vault Dweller fails a Speech check, refuses to pay caps to the raider, or simply decides to attack the raider, the raider will engage in combat with them. Upon killing the raider, the Vault Dweller will receive 400 XP (as opposed to 1000 XP for talking the raider out of killing Sinthia) and Marcelles' thanks. However, Sinthia will be enraged, saying that "you really don't care for Human life" and refuse to speak with the Vault Dweller.

Sneaky way
The Vault Dweller should talk to the raider in a peaceful manner. When the raider says he needs to think about it, the Vault Dweller should begin sneaking. If the Vault Dweller's Sneak 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"