The Morris home in Scranton, Pennsylvania.
Mink Morris - A seven-year-old playing the game Invasion.
Mrs. Morris - The mother of Mink.
Joseph Connors - An older boy who wishes to play Mink's game but is spurned.
Unnamed twelve-year-old - A friend of Joseph Connor's.
Anna - Mink's friend and assistant for the game. Drill - The supposedly imaginary friend running the game.
Pete Britz - One of the kids who're getting too old to play.
Dale Jerrick - One of the kids who're getting too old to play.
Helen - A friend of Mrs. Morris who lives in New York.
Tim - Helen's son, who's also playing Invasion with Drill.
Peggy Ann - One of Mink's playmates, who gets too scared to continue.
Henry Morris - Mink's father.
Mink Morris, who seems to be playing a game called Invasion.
Mrs. Morris, who refuses to take Mink's game seriously.
The game turns out to be a true invasion from non-Earthian creatures.
Hiding for their lives, Mrs. Morris and husband Joseph are found by Mink and her new invader friends.
Much like "The Veldt", the main theme of this story is the danger of the creative imagination. Related to this is the particular danger posed by children. Here it's not neglect that's at fault, but the common adult refusal to take the behavior of children seriously.
Mrs. Morris is amused at how excited her daughter Mink is about her latest game, Invasion. As adults go about their business, Mink and her friends gather objects for their game. Joseph Connors wants to join but at twelve is too old to play. Mrs. Morris watches as Mink and Anna writes notes and makes Mink slow down during lunch. Mink insists that Drill is waiting for her, though, and Mrs. Morris finds out Drill is the invader from someplace - like Mars but not Mars, Mink explains. The invaders couldn't figure out how to attack Earth but discovered they could use the fourth dimension and the imagination of children under nine. Drill promises the children a world where kids can do whatever they want, though some kids who are getting older - like Pete Britz and Dale Jerrick - have become snooty and will be the first to be killed.
At four o'clock, Mrs. Morris receives a call from her friend Helen in New York, whose son Tim is also playing the game of invasion and has an imaginary friend named Drill. Mink shows her mother a yo-yo that can disappear, something Tim also has. The day passes and Mrs. Morris sees Peggy Ann, a neighborhood girl, crying. She asks Mink what's the matter and Mink says she's scared; Drill is stuck halfway and as soon as he comes through, the rest can follow. Five o'clock finally arrives, the zero hour Mink anticipated. Henry Morris comes home from work and the two parents hear a buzzing followed by explosions that shakes the house. The children scream with delight but Mrs. Morris panics, dragging Henry with her to the attic where they can hide. They hear heavy footsteps and Mink calling for her parents; with her new invader friends, she finds her parents.