One idea could be that Percy is interrogated by the Olympians because they suspect him of a crime he didn't commit. Maybe they think he stole a powerful artifact. Another could be that he's interrogated by a new, shadowy organization within the demigod world that's trying to gain power. Or perhaps he's interrogated by an old enemy who has some new leverage against him.
A great plot idea for a Percy Jackson interrogation fanfiction would be that Percy is captured by a group of monsters working for a greater evil. They interrogate him to find out the location of Camp Half - Blood. The interrogators could use various cruel methods, but Percy stays strong. Another idea is that he's interrogated by the Romans because they suspect he's a spy for the Greeks. This could lead to a lot of tension between the two camps and some interesting character development for Percy as he tries to prove his innocence.
One plot idea could be Percy having to team up with Hera to rescue a group of demigods who have been captured by an ancient monster. Hera, despite her usual aloofness, realizes she needs Percy's unique skills.
Perhaps a fanfiction where Percy and Thalia are transported to an alternate dimension. In this new world, they have to figure out how to get back while also dealing with different versions of their friends and enemies. Thalia might have to face an alternate version of herself who has turned evil, and Percy could be the one to help her see the light again. It would be full of action, drama, and self - discovery.
A plot could involve Hera taking Percy on a journey through the past to show him the origins of the gods' power and how it relates to the current problems in the demigod world. This would give Percy a new perspective and knowledge that he can use to save the day. Or perhaps Percy accidentally stumbles upon a secret of Hera's that she's been hiding for centuries, and she has to enlist his help to keep it safe, all while other gods are trying to uncover it too.
Another plot idea could be that Percy discovers a hidden underwater civilization that is not related to Poseidon. This civilization has its own set of rules and powers. Percy has to navigate through their complex society and politics while also trying to convince them to help the demigods in a coming war against an ancient evil that is rising again. The underwater civilization could have unique magic and technology that the demigods have never seen before.
One idea could be that Percy has to face a new threat from Medusa's long - lost sister who has even more powerful petrifying abilities. He has to use his skills and some newfound knowledge about the Gorgon lineage to defeat her.
Perhaps there's a situation where a powerful deity wants to pit Percy and Clarisse against each other in a tournament. But instead of fighting, they decide to work together to outwit the deity. They train in secret, combining their different fighting styles, and in the process, they form an unexpected bond.
One plot idea could be Hera going on a quest with Percy. Since she's a goddess and Percy is a demigod, their dynamic would be really interesting. They could face challenges that test both Hera's divine powers and Percy's wits as a hero. Another idea is a story where Hera loses her memory and Percy has to help her remember who she is while protecting her from other threats in the demigod world. Maybe some monsters would see her in a weakened state as an easy target.
One idea could be Percy discovers a hidden section of the maze that leads to an ancient Greek library filled with forgotten knowledge. This knowledge could help him in his future quests.
One idea could be that Percy and his friends encounter Gilgamesh during a quest in a strange new realm. Gilgamesh could be a powerful ally or a mysterious foe. Maybe they have to work together to defeat a common enemy that is threatening both the world of Percy Jackson and the ancient lands of Gilgamesh.
One idea could be Percy having to work with Demeter to save a magical grove that's being poisoned. Demeter could be initially distrustful of Percy, but as they face challenges together, she realizes his worth.