Las huellas imborrables

Let sleeping dogs lie was one of the last things said by Britta, a childhood friend of Erica's mother, before she was killed. History professor Erik Frankel, who Erica had given a Nazi medal found among her mother's possessions, is also found dead a few days later. Why does her mother have the medal and what is the connection between the cruel murder of the professor and the tragic events of World War II? All the clues lead to a deep secret from the past.