Make things up as you go along, using the following as guidelines:
Agvhazar is an oasis on the world of Delta. Trading routes between larger cities cross here.
If you have an image of lakes and palm trees, forget it. It will probably be what the player characters are expecting, but it will not be what they get.
The desert sun is far too hot for standing water to remain in the open air. The source of Agvhazar's water is an underground lake. Above the lake, there is a huge rock the size of a small mountain, and it is this rock which keeps the lake relatively cool and stops the water evaporating.
The city of Agvhazar is built into the rock.
Social status in Agvhazar depends on how high up you live. The Caliph's palace is at the top of the rock.
If the player characters decide to recruit more adventurers to the party after arriving in Agvhazar, that is possible, within reason. This is, after all, a place where trading routes cross. All sorts of people might be passing through, for all sorts of reasons.
Just don't let it get out of hand. Although all sorts of people might be passing through, they won't all be passing through at the same time. It might, for example, be that although the party really needs an invoker, no invoker turns up in Agvhazar for several months.
However, character types who regularly accompany desert caravans turn up in large numbers, and it should be easy enough to recruit several of them.
Additional player characters may be added that this point (and in this plot-line this is the last point at which additional player characters may be added, since the real adventure is about to start). These additional player characters may be of any allowed combination of class, alignment and race, and must come up with their own reason why they happen to be passing through Agvhazar at this time.
Since the Caliph has completed an adventure, successfully navigating several difficult journeys by flying carpet and recruiting a number of bodyguards while simultanously not getting himself killed, we'll give him a rise in level.
(AD&D-Specific: ) Opryroman Masud, human male, 2nd level fighter, Str 18(98) Dex 7 Con 15 Int 9 Wis 10 Cha 14 Align LG Hp 13.
The most important person in Agvhazar is the Vizier, who (for once) is not the villain.
(AD&D-Specific: ) Omastam Edsul, Vizier of Agvhazar, devious but ultimately loyal. Human male, born in Agvhazar. Str 15 (Stamina 13, Muscle 17) Dex 11 Con 9 Int 14 Wis 9 Cha 13 Align NG Hp 56 Fighter, level 14. Since Edsul no longer engages in combat, he does not rise in level.
Edsul is elderly and old-fashioned. Although he means well, his advice is sometimes entirely inappropriate as he is not au fait with the ways of the modern world. He suffers from the additional fault of trying to be too clever. He knows that Viziers are supposed to be subtle and devious, and tries to be, but he is not really up to the task. In particular, he lacks imagination.
Since it was Edsul's well-meant but inappropriate advice which got the current Caliph's father killed, the Caliph does not trust his Vizier.
The harem includes a few wives and concubines (the Caliph does not have many of either). They are all 0th level humans. They are reasonably attractive, but none of them is stunningly beautiful.
The Vizier's one and only wife, Jecteelia, spends a lot of time in the harem. Her job is to advise the Caliph's wives, in the same way that her husband advises the Caliph. Her advice is somewhat better than his, as she is considerably younger than her husband, and understands the modern world better. She also suffers from the fault of trying to be too clever. Like her husband, she tries to be subtle and devious, but is not up to the task.
(AD&D-Specific: ) Jecteelia, wife of Omastam Edsul. Human female, born in Agvhazar. Str 16 (Stamina 18, Muscle 14) Dex 11 Con 8 Int 15 Wis 9 Cha 11 align CG hp 11. Mage, level 4. Since Jecteelia regularly uses spells as a part of her daily duties, she continues to rise in level, and does so fairly quickly.
There will be a few assassination attempts, although these are not the real plot. If there are female player characters sleeping in the harem, these assassination attempts will be easily foiled.
On the other hand, if all the player characters are male, one of the overnight assassination attempts succeeds. The player characters are now out of a job, and also have the problem of getting out of Agvhazar alive. A popular Caliph has been assassinated when it was their job to protect him.
The real plot is political. Do you think politics is boring? Not the way the rulers of Havdazar play it, it isn't.
The favourite hobby of the rulers of Havdazar is invading other countries. This year, they are going to invade Agvhazar. There's an army on its way.
That's right. An army. About eighty thousand Havdians, many of them full-time professional soldiers, are on their way here. They will reach Agvhazar on the next full moon. Depending on how generous the DM feels, that is anything from four days to four weeks away.
Sooner or later, someone will notice this army (it is not following the trade routes, and its progress is therefore slow, but even so it is difficult to keep an army of eighty thousand a secret for long). When they do, two things will happen.
Firstly, the Vizier will make a stereotyped and inadequate response. All adult males in Agvhazar will be conscripted into the army. This amounts to five thousand men with military experience (the citizens of Agvhazar are used to having to fight to defend themselves) and ten thousand others. Although it calls itself a city, Agvhazar is really just an oasis where trade routes cross.
Secondly, the Caliph will ask the player characters to defend the city. He does not trust his Vizier, and the Vizier has got off to a bad start by announcing an inadequate response. If there is a conflict between the Vizier's suggestions and those of the player characters, the Caliph will give precedence to those of the player characters unless and until they make mistakes as bad as those of the Vizier.
For those of you into such things, the army comprises the following:
A guideline for DMs:
There could be quite a lot of experience points in this for the player characters:
This is a particularly bloodthirsty scenario. If the invading army continues with an attack against an army of around thirty thousand experienced defenders (and they are fanatical enough to do just that), the overall casualties could end up approaching six figures.
Some of those casualties will have been carrying magical items, so for anyone prepared to search a lot of corpses, there will be a lot of magical items to be found.
It is also a scenario in which player characters can go in at low level and come out at a respectable medium level, with their names known world-wide, in the space of a few months of scenario time.
On the other hand, if they don't use their intelligence, the entire party could end up dead.