1: Guest quarters
2: Commandant's dinner
To find the Zhentil Keep outpost, travel along the shore to the west, past the buccaneer's camp. Eventually you will come to a strong-looking castle with armed patrols. Riders will be sent out to greet you, but if you tell them you are not the envoys, they will send you on your way. If you reveal that you are the envoys from New Phlan, the riders will escort you to the office of the commandant. He will review the packet you are bearing and then you will be given a tour of the place. Then you will be shown to your quarters where you are instructed to remain until dinner.
At dinner the commandant will subtly pump you for information on the status of New Phlan. You can feed him disinformation about the city and other topics, but if you talk about the Pool of Radiance he may relate journal entry 46 to you.
After dinner you will be escorted back to your quarters - make sure you post a guard. In the middle of the night four guards will enter your room and attack, after which a second wave of guards will attack. The best bet is to leave town. The inner keep is locked up tighter than a clam, so you won't be able to get inside there to get more information. You can either scale the walls to escape, or you can fight your way past guards at the front gate - either way is not too difficult. If you move around enough, you may run into the main group of guards led by a dwarf. It can be a tough battle, but fireball and hold person will go a long way in making it easier. The dwarf carries gauntlets of ogre power, chainmail +1, and a longsword +1. Immediately after that battle will be a second wave with the Commandant, the wizard Al-Hyam Dazid, and dozens of corporals and aides. Magic items from that battle are: wand of lightning bolts, 3 potions of extra-healing, 2 rings of fire resistance, a shield +1, plate mail +1, a longsword +2, and a set of bracers AC3. After killing the commandant, the rest of the outpost will flee.