The illustration shows an egg monster on top of a bunch of eggs in the kitchen.
Dana Johnson's little sister, Brandy Johnson is having her birthday coming up a week – which is the time that is before Easter. She cons her parents into setting up an egg hunt for her birthday. But during the party, an egg fight ensues and the party becomes a disaster. During the egg hunt, Dana finds a strange, large, pale green egg – which does not break when it is thrown by Dana's best friend Anne, much to Dana's amazement.
About a day after the egg disaster, the huge green egg hatches and out comes an "egg monster" that resembles a pile of rotten scrambled eggs with eyes.
Dana places the creature in a shoe box and bikes over to Anne's house to show it to her. Anne's mother is disgusted by the thing and nearly washes it down the drain, but it is saved by Dana. He later brings it to Dr. Gray's lab. Dr. Gray explains that the eggs came down from Mars in a shower that only hit the town. Dana's egg was the last one.
Dr. Gray locks both Dana and the egg creature in a room with frigid temperatures ‒ and the room contains many more egg creatures. He wants to keep Dana to experiment on him because of Dana's contact with the creature. Dana's father does not discover that he is there.
After a few hours, the egg creatures merge together to form a blanket for Dana so he does not freeze to death. Eventually, the creatures overpower Dr. Gray and Dana gets out of the room and runs back home. But when he comes back to the lab to show his parents the egg monsters, both the egg monsters are disappearing — so did Dr. Gray are gone. Also, his parents do not believe in him.
The next morning, he seems to be fine and begins to go to his friend Anne's house. Suddenly, he crouches on the lawn and lays an enormous egg.
- The cover makes it seem like the egg creatures are really monsters. But in the book, they're actually a benevolent force captured by a mad scientist (the only exception being that they impregnate other people to reproduce).
- Dana and Brandy's father was mentioned by name in the book: Clark Johnson.