Ordeal of the Viper (d20)

From the introduction:

An adventure for four 16th to 17th level player characters...The Lord of Envy has ruled Orland for many centuries. He was once a priest of Salystra, the Demon Serpent Goddess of his people, but he forsook her ways and betrayed his people long ago, turning to the worship of the Dark God Vornoth. He never took the tests that the Serpent Goddess puts all powerful drow through. Indeed, he was protected from her power by Vornoth, and through the god’s might rose to the rulership of Orland. Along the way he acquired the treacherous Chancellor Koorlsh, who learned of his weakness and seeks to exploit it to overthrow Garlgax and rule Orland in his stead. Koorlsh hopes to use the PCs as pawns in his game.