The concept of a game, or of play in general, is a powerful and important motif throughout the story. At first, the alien invasion unfolds only within the confines of the game, but as the plot progresses, the line between imagination and reality blurs. Bradbury’s use of this motif complicates the very notion of innocence and therefore furthers the story’s thematic concerns with its loss. It’s hard to tell the exact moment that the game becomes more than a game—in other words, when the game becomes something that is no longer innocent. The same can be said of the children themselves. As the game becomes more serious and the consequences more real, the children’s understanding of what they are ushering in seems to grow. The lack of a clear boundary between game and reality mirrors the lack of a clear boundary between innocence and culpability.

There are many moments within the story that mention a clock, the passage of time, or a reference to a specific moment—most notably the designation of five o’clock as “zero hour,” or the planned time of invasion. Phrases like “time passed” (Paragraph 158) and “the hour drowsed by” (Paragraph 143) keep the passing of time at the forefront of the reader’s mind, creating a countdown to zero hour.