The plot follows the lives of three female detectives who investigate the secrets of others, but end up uncovering their own families' lies and truths they would prefer to ignore.

Inés, Eva and Carmen, three women of different generations, work as private detectives for an investigation agency run by Valbuena, their male chauvinist boss.

Inés, the youngest and most ambitious of the three is assigned to work undercover as an employee in a factory to spy on the activities of its union leaders.

Initially, she hoped to move through the ranks by working on this case, but her plans go awry when she begins to empathize with and develop feelings for Manuel, one of the key union members she is investigating.

She follows him from Madrid to Zaragoza where she quickly finds out that he has had a son born from a previous relationship and has now become involved in the life of the child he ignored for 10 years.