It contains a fictional account of the Children's Crusade of 1212, as witnessed by Rudolf Hefting, a boy from the 20th century.

Rudolf "Dolf" Wega is a fifteen-year-old who volunteers for an experiment with a time machine.

He saves the life of Leonardo Fibonacci da Pisa, without realizing who he is, and teaches him Arabic numerals.

In the book, two slavers delude a group of children into coming with them with stories of how the innocent shall liberate Jerusalem.

It was shown at the Berlin International Film Festival in February 2007, and was released in other regions, in theatres or on DVD between 2008 and 2010.