Stuck with a quest - Suspicious guy and the amusement park

[karanus016]

After Noire is kidnaped by being accused to be a spy, I go to Lowee and talk with the "Suspicious guy". I chose to help him and now I don't know what to do. There is no quest from him in my quest log and when I go to the amusement park to save Noire, no event triggers so I am stuck

Help, please Q__Q

[Ztarman]

You need 5 Mysterious Grass which is found in Twin Mountains