What key event leads to the climax of the story?

The event that leads to the climax of the story is the Society's infiltration of the Learning Institute. This moment is pivotal because it sets the stage for the series of actions that culminate in the intense confrontations and revelations that follow. During this infiltration, the main characters—Reynie, Kate, Sticky, and Constance—face various challenges that test their skills, teamwork, and resolve as they work to uncover the dark secrets of the Institute.

The infiltration directly leads to the discovery of Mr. Curtain's true intentions and the pivotal confrontations that follow. It raises the stakes for the characters and engages the reader in the unfolding tension. This act is not only action-oriented but also serves as a critical turning point, where the children's motivations and the heart of the conflict are brought to the forefront, pushing the story towards its climax.