This is an idea for a Sertorius campaign set in the Marite Kingdoms, a cluster of walled city states united by the rule of the earthly qoddess Queen Sabeena. It starts out with the party being recruited to clear giant tribes from the surrounding hills but soon turns to political intrigue as internal conflict explodes within the Queen's inner circle of Sertori-Advisers.
Queen Sabeena is a powerful monarch who achieved her father's dream of uniting the Marites under a single ruler. A sertori, she used her powers to defeat her father's remaining enemies and force all the Marite cities to acknowledge her supremacy.
However her reign has only just begun and she relies on an inner circle of Sertori advisers whom she deals with cautiously. In recent months, she suspects some of them are plotting against her. She is wary of directly challenging them (they are Sertori after all). So she devised a scheme to recruit allies without attracting their suspicion. In the wake of rumors that a new deposit of silver was discovered in the Aqaban mountains, she announced her desire to hire giant killers to clear a safe route for scouts and miners. Specifically, she wanted Sertori giant killers and said she wished to recruit outside her inner circle to avoid unnecessary risk. Since few of her advisers possess combat magic, they were pleased with this course and immediate sent word that Queen Sabeena was hiring Sertori.
The players receive Queen Sabeena's message. Should they respond, they will need to travel to the city of Besra to appear before the queen. If they impress her, she hires them and they will have several adventures dealing with giant tribes and grim in the foothills of the Aqaban mountains. The more successes they have, the more titles and responsibilities she will bestow upon them.
Over the course of their campaign against the giant tribes, if they take the time for diplomacy, they will learn that a number of chieftains are willing to work with Queen Sabeena for the right arrangement. The giants themselves are aggressive and dull-witted but not evil by nature. They will meet good giants and they will meet bad giants, but the sentiment in Besra itself will remain unsympathetic. It is even possible the player characters may decide to join with the giants against the queen.
Once Queen Sabeena is convinced they can handle the task, she will use subtle means to convey her plans to them. Essentially she wants the party to assassinate her existing council of Sertori and act as their replacements. Because they could fail, she doesn't do this with direct messages but tries to express her plan with hints here and there over a period of time. If they succeed, they find themselves in the middle of the Queen's Court and the campaign turns toward politics in the city of Besra. The Queen is ever cautious and the players will have to work hard to not attract her suspicions themselves. If they fail, the Queen cannot help them or acknowledge her role in their mission.
To succeed against the council will be more difficult than imagined. One of the councilors has allied with a Grim that appeared as a dense mist in the city of Shanor. There is an intelligence at the heart of this grim and it is feeding resentment against the Queen. What is more alarming: the Grim Appears to have unnatural control over all water in the city. It can use water as a medium through which to launch its attacks or use it directly to drown its enemies. It can even summon rain and flood the streets. What is at the center of this Grim and what its true nature is, are mysteries for the GM to flesh out.