Paulina, a fifth-grader, spends her free time writing exciting detective stories and is always on the lookout for a new mystery to solve. When her grandmother mysteriously disappears, the undaunted Paulina decides to take the case on herself. The investigation gets off to a thrilling start when the sharp-eyed Paulina notices that her grandfather is hiding something.

Soon, however, Paulina realizes that her grandmother hasn’t disappeared at all—she has developed Alzheimer’s disease and no longer remembers her family. Paulina is faced with a completely new kind of mystery: how can she get to know her grandmother all over again when her grandmother doesn’t remember her and seems to have changed completely? At the same time, Paulina’s life is also complicated by parents who demand good grades, strict teachers, and Marta, who bullies her at school. Will her detective skills be of any help when what she has to solve is something much more personal?