Kristy and the Missing Child is the fourth book in the Baby-sitters Club Mystery series.
At the end of Krushers baseball practice, Kristy is getting ready to walk home with David Michael and Bart Taylor and is surprised when she notices Jake Kuhn walking home by himself, but Jake says he got permission from his mom to walk home by himself while she takes his younger sisters Laurel and Patsy to the dentist and Kristy doesn't think anything of it.
Later that evening, Mrs. Kuhn calls Kristy to tell her that Jake never made it home. At first she thinks that Jake went to a friend's house, but after some phone calls, nobody has seen Jake which prompts Mrs. Kuhn to believe that her ex-husband possibly took him. The divorce was recent and the kids have been missing their dad a lot.
Despite Mrs. Kuhn's claims that her Mr. Kuhn is responsible, nobody else is quite as sure because Mr. Kuhn was well-liked and the divorce was relatively friendly. It appears to be unlikely that he would kidnap his own son. Kristy knows that everyone needs to consider the possibility that Jake might be hurt somewhere, so she puts together a huge search party. She also feels responsible for Jake going missing because she was the last one to see him before he went missing.
The first day of the search party doesn't turn up much. Kristy has Matt Braddock in her search group and Matt knows all sorts of secret places that Jake might be, but he isn't in any of them. Meanwhile, the police are still pursuing the fact that Mr. Kuhn kidnapped Jake and think it he might be in Mexico.
Despite Kristy feeling hopeless, she is determined not to give up and continues to find Jake. When Kristy goes out searching with the Braddock kids, Matt remembers a construction site where some houses are being built & where Jake liked to go and get some scrap lumber.
When they go over to the construction site, they discover that Jake had fallen through a hole in the floor of one of the houses being built. Bart runs to get help, Jake is rescued and reunited with his family.
Mary Anne has a hard time in her home ec class at school, but is able to pass the class by making Jello Jigglers. In the end, Mary Anne ends up receiving an award for "Most Improved Home Ec Student." The last award was for Kristy. It was because Kristy found Jake. Right before Kristy got the award, Bart kissed her on the lips.
Kristy can hardly believe it when little Jake Kuhn is reported missing. Jake is one of the kids on her softball team. And Kristy was the last person to see Jake before he disappeared.
Even though the Baby-sitters and all Jake's friends are helping look for him, Kristy still feels horrible. And when the police can't find Jake after almost two days, things look really serious.
Kristy knows she's just a kid, but she's determined to find Jake. Wherever he is...