From the web:
Moonshae is a supplement which details the Celtic-inspired islands in the Sea of Moonshae, setting for the novel Darkwalker on Moonshae and its sequels by Doug Niles,describing the climate, topography, and economy of the region,including the Korinn Archipelago, which was created by Aaron Allston and first detailed in the module N4 Treasure Hunt. It also details two regional cultures and their lands: the indigenous people known as the Ffolk, and the invading Northmen.
The book discusses the character races, character classes, politics, conflicts, geography, and economics within the Moonshaes. The islands are home to the Ffolk, a druidic people who worship the Earthmother, a neutrally aligned aspect of Chauntea,
the neutral-good goddess of agriculture. The Ffolk share the Moonshaes
with the Northmen, a strong, warlike race of raiders who hail from the
lands north of Waterdeep. Conflicts frequently erupt between the two
races, as the Northmen expand their holdings on the Moonshaes at the
expense of the Ffolk. Magic-users are viewed with suspicion by both groups. The Moonshaes are also home to marauding firbolgs, orcs, goblins, trolls, and other more dangerous monsters.
The book next describes the major supernatural entities which
exist in the countryside and seas. The most important of these is the
Earthmother. She gives life and vitality to the land, and her power is
manifested in the Moonwells. The Moonwells are pools of water with the
magical power to cure the wounds of those who strive to maintain the
"mystic balance", and are tended by druids who can use them to charge or
restore charges in magical items. The Earthmother is served by her
three immortal children: Leviathan, a huge whale; Kamerynnm, a majestic
unicorn; and the Pack, a pack of dire wolves who roam the Isles. They
are opposed by the evil Kazgoroth the Beast, who seeks to disrupt the
balance and bring corruption to the Isles, aided by its magically
created Blood Warriors: undead soldiers who obey its every command.
Several specific locales of the Moonshaes are also described, from the perspective of Elminster as a tour of the people and places he has visited. The style of presentation is similar to that used in the Forgotten Realms Campaign Set.
The 64-page booklet comes wrapped in a removable cover. Included with the book is a fold-out color poster map of the Moonshae Isles,
which lie to the west of the main continent of the Forgotten Realms
setting. This large color insert has maps of the Moonshae Isles printed
on both sides. One side is at a scale of 20 miles per inch, while the
reverse is scaled at 30 miles per inch. Both maps contain the same
amount of detail, the major difference being that there is less open sea
surrounding the 20-miles-per-inch map. One of the maps lines up with the edges of the maps in the Forgotten Realms Campaign Set. Two appendixes explain using the Moonshaes in a campaign and the magical items of the Moonshaes.