Lotte and S?ren Hammer are a sister and brother from Denmark. Younger sister Lotte worked as a nurse after finishing her training in 1977 and her brother S?ren was a trained teacher and a lecturer at the Copenhagen University College of Engineering. After S?ren moved into the house where Lotte lived with her family in 2004 they began writing crime novels together. To date, they have written five books in this series. The Hanging is the first and The Girl in the Ice the second.