The Secret Apartment

Jillian's summer takes a turn when her mother's remarriage forces her to leave Pennsylvania for a cramped New York City apartment and a new stepsister who seems determined to make her life miserable. Just as she's resigned to endless camp activities, she's asked to catsit for the elderly neighbor in the penthouse, a job that opens a door to a hidden mystery right in her own building. With the help of a few new friends, Jillian discovers that the ordinary apartment complex holds a secret that could change everything. The story blends family adjustment, city adventure, and a puzzle that drives the narrative.