A young girl's impulsive decision to entertain a mysterious stranger leads to a dangerous intrusion into her family life. Alice, feeling alienated at a family gathering, initiates a charade by welcoming a girl who claims to be an old acquaintance. As this newcomer systematically integrates herself into the household, Alice realizes the stranger's presence is not a harmless prank but a calculated infiltration. The narrative follows Alice's growing suspicion and her struggle to expose the intruder before her own position within the family is permanently usurped.

Readers and critics frequently highlight the book's accessible prose and its ability to capture the nuances of teenage social dynamics. Discussion often centers on the effectiveness of the suspenseful atmosphere as the intruder slowly dismantles the protagonist's sense of security. Reviewers note that the character development feels authentic, particularly in how it portrays the frustration of feeling overlooked within a family unit. The pacing is widely praised for maintaining interest while balancing humor with the darker elements of the mystery. Overall, the work is recognized for its realistic depiction of adolescent growth and the complexities of interpersonal relationships.