Aran's tasks to receive the Shadow Thieves' aid

Aran's tasks to receive the Shadow Thieves' aid is the main quest of Baldur's Gate II Chapter 3 if you've sided with Aran Linvail and the Shadow Thieves instead of Bodhi and her vampire guild. There are three tasks that must be performed in order for the party to receive Aran's help in reaching the island of Brynnlaw. 
Your initial meeting with Aran leads to the following Journal entry in the quest section:
==Task No.1 — Mook==
Go down to the south end of the Docks District at night and meet with Mook at the Shipyard Docks. She will fill you in on her previous encounter with a strange man that she's observed casing the area. A cut scene will begin and a creature named Lassal will appear. Mook will attempt conversation and Lassal will kill Mook and attack your party. When Lassal reaches a low enough hit point level, he'll revert to his gaseous form and leave. 
This leads to the following Journal entry:
When you return to Aran and report what took place, he seems genuinely bummed that she was killed. He'll then task the party with finding the vampire's lair by posing as enemy recruits to two traitors named Caehan and Jaylos, who are going to meet with a contact from the rival guild on the second floor of the Five Flagons Inn.
This leads to the following Journal entry:
==Task No. 2 — Jaylos and Caehan==
Go to the second floor of the Five Flagons Inn and look for the two traitors. Conversation will either lead to them believing your story of being other recruits or attacking you. During the beginning of the fight, Caehan may blurt out the name of the guild contact (Gracen). The guild contact will also arrive and ask what's going on. Depending upon your charisma, he'll either tell you the location of the guild or attack. He carries a note from Lassal that also provides the guild location. 
This leads to the following Journal entry:
Return to Aran and inform him of what you have learned. He'll inform you of Bodhi's attack upon the guild and send you to the Graveyard District to destroy Bodhi and the vampire guild.
This leads to the following Journal entry:
==Task No.3 — Defeat Bodhi and her guild==
Go to the Graveyard and head for one of the three entrances that leads to the Lower Tombs. Watch out for a potential appearance of Pai'Na's spiders (should they randomly spawn again), and then meet up with the mage Haz and his flesh golem near the entrance to the vampire guild hideout. Defeat the Grimwarders and Fledgling Vampires, then go after the remaining mature vampires. Defeat Durst, Gellal and Lassal and stake all three of them in their coffins. When you have finished staking Lassal, Bodhi will appear and after some conversation, she will attack. Once she's lost enough hit points, she'll turn gaseous and flee. Return to Aran and make a report.
This leads to the following Journal entry:
Return once more to Aran and he will set you up with Saemon Havarian who will captain the ship that will take you to the island of Brynnlaw.
This ends the quest with the following Journal entry: