[Link]

OK, so the basic outline of the plot (as I see it) is as follows.

~ ~ ~

Gaelan Bayle sets you up with the Shadow Thieves, but you can choose an alternative. A vampire named Valen approaches you and tells you there's she can help you get to Spellhold as well.

While Gaelan Bayle has directed you to the Docks district, Valen points you to the Graveyard district. So the path splits up:

1)Enter Docks District
NOTEThe incident with Renfeld should of course change for the following to happen. What I suggest is not a timer, but more like a cutscene when the player is going to travel to the Docks and hasn't been to the Graveyard District before. On the way to the Docks the player will come across Renfeld and his attackers.

~

As you enter the Docks district, you are hailed by a woman (any given name, but let's call her Asheera). She tells you about Xzar, a known Zhentarim and necromancer. Now of course Asheera knows this information, and so do her friends, but the law prohibits them from killing him on the streets. So she wants you to play the game along [what follows is the Quest for Montaron's body]. As we all know, Galvarey and his follower aren't true Harpers so that's why Asheera tells you not to mention her name or that you've talked to her.
If you finish the quest in a good way for the Harpers, you've proven your interests to them (on both sides, Galvarey AND Asheera), but they still remain rather vague about it all. Asheera will only tell you "They are watching you with interest and caution alike, my masters. You will probably hear from us, but know this, . Those who have contacted you before are not to be trusted." Galvarey will go on with the usual Harper business that is own to the original Shadows of Amn.

~

The second time you meet Asheera is when you've mentioned her name to Galvarey (if Jaheira is in the party she will advise to go speak to Galvarey} or when you've tried to side with the Shadow Thieves or Bodhi. In case of the first, Galvarey will not know who Asheera is and warn the player about her. "She is not a true Harper, that is one thing which is obvious." Asheera will then once again contact the party, telling them they were careless by mentioning her name, to which the player obviously responds "You proposed a deal, and we wanted to contact you again. How else could we have done that?" This insightfulness impresses Asheera so she proposes a task [insert new quest here]. If the player accomplishes this task, they will meet Asheera in [insert building here].
Successfully accomplishing the task means and answering some of Asheera's questions means you've sided with the Harpers. Come to the building otherwise, and Asheera will leave never to return again. This leaves only Bodhi and the SThieves open.

~ ~ ~
2)Enter Graveyard District
Upon entering the Graveyard district you immediately meet Bodhi. Bodhi tells you the usual and says you should travel down the crypts to meet her. When she disappears, and you travel further across the Graveyard you walk into a fight between a vampire and three Shadow Thieves. Whatever the outcome, one of them will survive, but will be killed by a man named Akur. He will be hesitant to drop his guard towards the player "for only vile creatures dwell the Graveyard at night. Even these dispicable thieves." When the player asks him about this, he gives him the same treatment as Asheera does ("They are watching you with interest and caution alike, my masters. You will probably hear from us, but know this, . Those who have contacted you before are not to be trusted." He then gives the party a cryptic note, somewhat like a riddle. "Solve it, he says, and you will find your answers." Then he disappears. Of course the answer to the riddle is relatively simple, and you end up in the same house Asheera directed you to. From here the path goes the same as mentioned above.

~ ~ ~ ~

The whole Harper ideology behind the matter is Irenicus and his thirst for power. They know his background, through Elminster of course, and they fear what might happen. So they want the player to stop him, and getting to Imoen means getting to Irenicus. At the same time they're anxious about as well. Gorion was a Harper too, so they know a great deal about you as well. They fear you may become to powerful at one point, so they wish to monitor you from close distance [maybe a new Jaheira sidequest here?].
Gaining your trust, and their trust is the main thing that the player has to do in his dealings with the Harper. Of course, this involves quest, but will learn more and more about both Irenicus, Imoen and his role. Not too much, because the Harpers still have their own plan.
The Harpers will let you travel to Brynnlaw by boat as well (Saemon again) and from there on the same thing happens.

~ ~ ~

In regards to the relationship with the Shadow Thieves and Bodhi, only Bodhi will actually be an enemy to you. The Shadow Thieves are only interested in Bodhi and her little guild, and only when staps in and mingles with their business will they become enemies. Other than that they will remain neutral, to an expense of course. If you don't watch your back, you could have two of Athkatla's largest groups on your hide.