Just to be really sure, once a King's Court card is with on an investigator, the only way to get rid of it is to use it, right ? Can it be activated if there is no effect (just to get rid of it) ? We played no, but without being totally sure…
During our last game, the keeper gave them early on in the game. The investigators then decided to split the party so the keeper could not use them anymore. Consequently, investigators where immune to cultists … tough game for the keeper.