GameSpot's nice History of AD&D gives a good overview of Curse of Azure Bonds as follows: "Published in 1989, Curse of the Azure Bonds followed the story of Pool of Radiance with more monsters, treasure, character classes and level caps. Shortly after the defeat of Tyranthraxus the Flamed One and the destruction of the Pool of Radiance, the heroic party was waylaid, knocked out, and marked with the five mysterious azure bond images stamped just beneath the skin of each adventurer's arm. Your characters recovered consciousness in the town of Tilverton on the Dalelands. Before they could even begin to ascertain who or what had attacked them, they found themselves compelled beyond their will to attack the entourage of a false prince and were beset by the city guard. Fleeing to the thieves' guild beneath the sewers, the members of the party would then begin their arduous quest to hunt down the creators of each of the five magical bonds and ultimately free themselves of the curse.
In terms of gameplay and structure, Curse of the Azure Bonds followed its predecessor more or less directly, though it broadened the path considerably. The already solid game system of Pool of Radiance benefited greatly from material that had hitherto been conspicuously missing, including the ability to advance to tenth level for clerics and eleventh level for magic-users (which meant that spells of up to fifth level were available), the ability to enlist characters of the more esoteric AD&D Paladin and Ranger (and with the latter, the line of Druid spells) character classes, and the option for human characters to dual-class."