Excited about trying to known everything about the Martians, Papelucho decides to catch one by using his experiments. One day, Papelucho surprising finds an actual Martian called Det, a Martian children, who is extremely curious about the humans and without thinking, he decide to introduce himself on Papelucho's body.
Papelucho starts to live with Det inside his veins and establish a deep friendship with him, but he finally think that Det cannot live in Earth anymore and needs to return to Mars. For that purpose, Papelucho starts to build a spaceship for fly to Mars and bring his friend back to home without knowing what will happen to him.
Papelucho series is one of the most popular children's book in Chile. Cine Animadores, after their local success with Ogu and Mampato in Rapa Nui started the production of the film in 2005 with the financial help of Canal 13 Films, using 1.5 million dollars in budget. The most notable difference between Papelucho and the Martian and Ogu and Mampato in Rapa Nui is the use of CG scenes mixed with traditional animation at the same time.
The film was very loosely based on the book of the same name Papelucho y el Marciano written by Marcela Paz in 1968 because is one of the most popular books of Papelucho line and also because of his sci-fi themes. The film was fully animated and produced in Chile, but it was dubbed in Mexico with recognized voice actors like Marina Huerta, Mario Castañeda and Maggie Vera, although Mexican voice actors maintained some Chilean Spanish slangs.