The return of Lucas tells the story of a well-off family who loses his eldest son, Lucas, 4 years old on the beach. Elena, his mother, is obsessed with finding him because he feels he is alive and never stops looking for him, neglecting his other children, Catalina and Juan, and her husband, Reynaldo, who took charge of the family and the company. After 20 years of the disappearance of Lucas, a photo of his son arrives at the mother's hands. A new track to follow that renews Elena's hopes of finding her son. Until one day, a young man shows up at the house of the Diaz Ayala family claiming to be Lucas. Will he be his lost son?