Caroline B. Cooney's The Face on the Milk Carton tells the story of Janie Johnson, who discovers she is Jennie Spring, a teenager who was kidnapped at age three and raised by Mr. and Mrs. Johnson.

As the story begins, Janie is enjoying being a teenager and spending time with her boyfriend, Reeve, and her best friend, Sarah-Charlotte. At her core, she is a caring, light-hearted person just coming into herself.

Janie is suspicious of the fact that she may have been kidnapped. Although she desperately hopes that it is not true, she cannot help but continue to search for the truth.

Janie is fiercely loyal to her parents, the Johnsons, even when faced with mounting evidence that they may have kidnapped her. She fights to return to live with them even after she knows the truth about who she is and where she comes from. When her parents begin to believe that Hannah may have kidnapped Janie, they insist on contacting the Springs despite the fact that Janie is terrified of being separated from them.

Janie feels guilty about her obsession with the kidnapping, and later, when she learns that Hannah tempted her with ice cream, she feels guilty for being so easily lured away from the Springs. She is torn between the two families.

The months of introspection cause Janie to find it difficult to focus on anything else. When Sarah-Charlotte wants to discuss boys, Janie is unable to concentrate, and it creates a rift in their friendship. Reeve gives her an ultimatum: to either tell her parents about the kidnapping or their relationship will end.

The guilt and stress of the kidnapping revelation have affected Janie physically as well as emotionally. She has not taken good care of herself and has failed to eat properly, which adds to her distress, especially as she loses a letter she wrote to the Springs that she fears will be mailed.

When the story begins, Janie is a fun-loving, silly, dreamy 15-year-old girl.  She yearns for romance and excitement, and attempts to make herself seem more exotic by altering her name on school papers (i.e. Jayyne Jonstone).  She is very close with her parents, and perhaps a bit spoiled.  Physically, her most striking characteristic is her head of unruly red hair.

As the story's plot develops, Janie becomes fixated on her kidnapping and stops being (and having) fun.  She is too self-absorbed to recognize and fulfill the needs of the people she loves.  Her inner turmoil causes her to lash out at those around her.  Inwardly, she is judging herself harshly for being a selfish daughter who could be bought from her biological family with ice cream.  However, the experience ultimately causes her to realize how great her love for her parents is, and what a wonderful life they have given her.