Garadon Manor is a d20 System scenario for three to five 6th- to 8th-level characters. Part of AEG's Adventure Keep line of short, cheap modules in half-sized format (4-1/4"x11"), it is intended to be run as a single session. From the back cover:

The legend of the realm of Tirna'cel is well known. Once remembered for its power-mongering warlords, homunculi-wielding sorcerors, and archfiends from the deepest pits of the Abyss, Tirna'cel has become a powerful and welcoming land over the last 600 years, due in no small part to the efforts of the warlord Tirna'gael, a member of the land's founding nobility.

But your party knows the truth. You ventured into the Tomb of Tirna'gael some six months ago, and therein discovered that the fallen warlord was actually little more than his brethren: a petty, avaricious power-monger. Possessed by a rival force which also desired the kingdom — a rare incorporeal demon called a nescent, which inhabited his body and augmented his already incredible power to unforeseen levels — Tirna'gael sought to overthrow the ancient warlords only to replace them.

Through Tirna'gael's augmented body, the nescent overwhelmed and eliminated the other warlords, eventually dominating the realm alone. But before it could consolidate its rule and throw Tirna'cel into an even darker age, the secret of its power was discovered by the paladins of Garadon, a virtuous cell of justice and light. The paladins lured Tirna'gael into the center of his own fortress and trapped him there within a powerful antimagic field. His body withered and died but the nescent remained dormant, waiting for its chance for revenge.

During your visit to Tirna'gael's fortress-tomb six months ago, you accidentally released the nescent from its prison. That enemy has since been vanquished — at least for a time being — but the memory of your pitched battle against it still lingers as you approach the original chapter house of the Order of Garadon.

You have been summoned.