Helviane is found behind the counter at Desele's House of Earthly Delights in Suran, and at first refuses to pay the debt money. If you raise her Disposition high enough (75), she will eventually agree to pay and give you the money. You can also try to pickpocket her. Otherwise, kill her and loot the money from her corpse.
Once you have the debt money, return to Eydis for an increase in faction reputation, and half the debt, 100 gold.
If you talk to Percius Mercius in Ald'ruhn about this quest, he has doubts whether this contract is legitimate or not and suggests that you pay the debt money yourself.
If you mention it to Manos Othreleth, he will thank you for your work, but won't provide any additional reward.
You can kill Othreleth without repercussions, sell his armor (and keep that nice sword of his), and then follow Percius Mercius' advice to pay the debt money yourself with what you've earned from selling the armor, without actually having to spend any of your money. This makes it a bit of a paradox, however - you're killing the person that the money is supposed to go to, so that you can get the money owed to that person.
If you have the Morrowind Patch installed, you will not receive this quest if you complete the Thieves Guild Bitter Cup quest prior to receiving this quest from Eydis, much as The Code Book is skipped.
If you kill Helviane at any point before or during the quest, Eydis won't give you any reward, although the journal text implies that she does.
You can give the money to Eydis only after speaking with Percius about the subject, or after actually collecting it.
If you have already spoken to Percius Mercius about Lirielle's Debt, the subject of "debt money" will trigger his response to that quest, not Desele's Debt, making it impossible to get the conversation where Percius doubts whether the contract is legitimate.
If you first pickpocket Desele, and then raises Desele's trust, and then ask for the debt you wil have double money 2x 200 . ?
The following Journal ID and Index codes can be used with the Journalconsole command to manually update the quest to a certain point.
Desele's Debt (FG_DeseleDebt)
Index
Finishes Quest
Journal Entry
10
Eydis Fire-Eye told me that Helviane Desele in Suran owes Manos Othreleth 200 gold. I must get this debt money from Desele and return it to Eydis Fire-Eye.
30
Percius Mercius suggested that I pay the debt money myself.
70
Desele agreed to pay the debt.
100
Finishes quest
Eydis Fire-Eye gave me my share of the debt money.