How powerful am I?
You're a first level adventurer (or NPC class) who never really got the hang of the life. Maybe you got scared or made a horrible mistake but you've been caught before your deeds are anything to boast about, and even in prison, your main claim to fame is that no one's killed you... yet.
How evil can I be?
You can be evil enough that your crimes earned you life in prison, but the year is 4000 - the Whispering Tyrant recently ran these lands and justice, such as it is, favors brutal effectiveness over opportunities for reform. Think fallen paladin to common criminal and avoid evil mastermind levels of evil. Necromancy is likely to get you killed before you even leave the prison grounds. A cleric of Norgorber may survive the initial interview, but a cleric of Father Skinsaw likely won't.
What if I choose to escape?
Your character will have a Mark of Justice on you that keeps you honest to the task.
What if I try to kill the paladin?
I wouldn't expect you to be successful but there's worse things to be said over your grave than 'They tried.'
What about gear?
You can politely request anything, but the paladins may not show you much mercy if you request something outlandish. Gear will be provided from the effects of the paladins, the prison effects room, and local shops. The town isn't much and you're not, either, so keep it to +1 weapon or lower price (overall). If you want to have masterwork full plate and a masterwork weapon, that's potentially available.
If the paladins are so noble and powerful, why don't they go alone?
The paladins didn't spend a long time learning languages. One of you is the interpreter, the rest of you are the bodyguards for the interpreter, and the paladins are your keepers not your protectors. Should (when) combat break out, they are going to spend the first round trying to offer mercy, the second round waiting to see if there's any hint of an opportunity to sway the hearts and minds of the enemy, but they wish to avoid personally killing as many of the enemy as possible so as to increase the chances of a peaceful resolution when the appropriate echelon of the enemy forces is reached.
Enemy?
Goblins seem to have taken over a fortress. The paladins are unsure if they actually drove out the people living there or took advantage of open gates with four stout walls, but the more information that can be gained about the events that lead to the fort being overrun by goblins, the happier the paladins will be.
Am I going to survive?
Maybe. Goblins can be brutal creatures and while the paladins will stabilize you, they may not raise you from the dead.
Recommendations?
Bard or another class that could potentially Aid Another on the paladin's Diplomacy attempts as the interpreter. Anything without a rage class feature is recommended. Sarenrae or another merciful deity is encouraged - you don't have to have E in your alignment to end up in prison.