Crusade in Jeans (1973) is a children's novel written by Thea Beckman. It contains a fictional account of the children's crusade of 1212, as witnessed by Rudolf Hefting, a boy from the 20th century. The original Dutch title is Kruistocht in spijkerbroek. A film version was released in 2006. Plot summary Rudolf "Dolf" Wega is a fifteen-year-old who volunteers for an experiment with a time machine. The experiment goes well, but accidentally Dolf is stranded in the 13th century. He saves the life of Leonardo Fibonacci da Pisa, without realizing who he is, and teaches him Arabic numerals. Together they join the German Children's Crusade, and through his modern-day knowledge, Rudolf manages to save a lot of children from horrible fates. However, his knowledge also leads to accusations of witchcraft. In the book, two slavers delude a group of children into coming with them with stories of how the innocent shall liberate Jerusalem. Their actual intent is to sell them as slaves for profit. With the aid of his twentieth-century knowledge and skepticism, and the aid of a "magical" device or two (such as a box of matches), the boy manages to keep most of the children alive and eventually gets them to safety. Characters Dolf Born in Amstelveen, his full name is Rudolf Hefting, and at the age of 15 becomes the active leader of the crusade. Leonardo Born in Pisa, his full name is Leonardo Fibonacci. He is a very intelligent young man and one of the few historical characters in the book. The historical Fibonacci is often considered one of the greatest mathematicians in the Middle Ages. Marie She is eleven years old, as stated by Leonardo. She is a parentless beggar with a very sensitive nature, and, during the crusade, both Dolf and Leonardo grow very fond of her. Frank The twelve-year-old son of a tanner from Cologne. Peter A strong child around the age of twelve, who, in the Crusade, became responsible for fisheries. After the tragedy in Genoa, his personality became colder. Hans His knowledge of the trees seems unlimited, as his father was a woodcutter. Bertho A tall and strong boy who felt a strong sense of guilt about his past. Everard One of the main hunters, along with Carolus and Bertho. In his life he has seen nothing but forests and hunting parties. He dies bravely in a fight between the farmers