The basis of the game is that you will control a party of young characters of various professions and races who are just starting out in life. At the same time, the city of Phlan is trying to rebuild. Your characters' main job (which is given to you by the city council) is to cleanse the slums of monsters. The more monsters you kill in each area, the less frequently they appear which is very frequently at the beginning. After you successfully clear each section, return to the city council, and they will reward you.
They also reward you when you do 'good deeds' by your own accord...if you clear the library before given the task to do so, or if you find the boy before asked. These serve as some very nice miniature quests and side quests with which to boost your experience and excel more quickly in the game. They are also nice as a distraction or to tackle when you are not quite strong enough for the next level of slums.
After you clear the slums, the city council will have other areas that need cleared out, Sokal Keep, the Mansion, the library, the graveyard, take the gate, stop the lizardmen, stop the kobolds, check the auction. And after your name gets more well
known, others seek your help, A Bishop of the Temple of Tyr, and a councilman. You will become famous in Phlan.
Other jobs you take on yourself. They consist of cleaning out the Pyramid, rescuing a royal kid with a heart shaped birthmark, and delivering a message to Zenthil Keep. It’s a trap, so be alert!
During all this, you've received hints about the leader of the monsters, and need to confront him to end his threat to New Phlan.
The thing I liked the most is that you can continue your characters into the next games. After this is Hillsfar or Curse of the Azure Bonds - whichever you choose. Either way, you loose all your money and equipment when you go into Curse, but the ability to export characters (that you have invested half your life into and are truly in love with) to the following game is still great.