You'll first meet Nalia in the Copper Coronet in the Slums District. She'll ask you to help her liberate her family keep from invading trolls and yuan-ti. This quest is covered on the de'Arnise Keep page. You'll successfully free the keep, but unfortunately you won't be in time to save Nalia's father's life. Afterwards, you'll learn that Nalia is betrothed to Isaea Roenall, but that she'd do just about anything (like give you control of her keep if you're playing a fighter) to dodge that marriage.

At some point later, a messenger will come up to Nalia and inform her that her father's funeral is about the start in the Graveyard District. If you don't make your way there within three days, then Nalia will give you a warning, and if you continue to ignore her quest after that, then eventually she'll leave your party and attend the funeral on her own. But luckily, afterwards she'll return to the Copper Coronet and become available as a companion again, so if you neglect Nalia, you won't really lose anything.

When you arrive at the Graveyard District, a messenger will take you directly to the funeral. While there, you'll meet a couple of well-wishers -- plus Isaea Roenall and his father Farthington. Isaea won't have anything to say to the likes of you, but when he sees Nalia, he'll chastise her for "slumming," and he'll continue to press her for their betrothal. At the end, he'll threaten, "This is unfinished." If you let Nalia go to the funeral on her own, then when you talk to her later, she'll just summarize what happened.

A day or so later, Isaea will stop you and arrest Nalia for being a "danger" to herself and her lands. You won't be able to do anything to stop this, but almost immediately afterwards, a guard named Khellor Ahmson will come up to you and give you a way to get Nalia back. He'll tell you that Isaea abuses his position all the time, and that you might be able to use this to your advantage. He'll then tell you two places where you can learn more about Isaea's wrongdoings:
  • Talk to Barg in the Docks District. You'll find him at the bottom of the stairs by the Sea's Bounty Tavern. Barg will be drunk and talkative, and he'll quickly reveal that Isaea is involved in piracy and slavery. He'll also tell you that Isaea's slaver contact is a man named Dirth.

    You'll find Officer Dirth on the lower level of the Sea's Bounty Tavern. If you talk to him then he'll attack you, and you'll earn 3200 xp for killing him. You'll also find Isaea's Slavery Document on his corpse. If you don't want to fight Dirth, then you can also just pickpocket the document from him.

  • Search the Roenell estate in the Government District. It's located at the northern end of the district, right next to the Council of Six building. Thanks to Khellor, the front door will be unlocked. Inside, you'll find Isaea's Financial Statements, which will indicate that Isaea has been smuggling gems.
When you bring this evidence to Corgeig Axehand -- Isaea's superior -- in the Council of Six building in the Government District, Corgeig will start an investigation, and he'll free Nalia in the interim. This will earn every character in your party 7000 xp. Isaea, of course, will be furious, and he'll threaten you again. However, this is the last time you'll see him.