Books can be attributed to "Unknown" when the author or editor (as applicable) is not known and cannot be discovered. If at all possible, list at least one actual author or editor for a book instead of using "Unknown".
Books whose authorship is purposefully withheld should be attributed instead to Anonymous.
The story is worth five stars, but I've knocked one off for the translation. I'm not qualified to comment on the technical quality of the translation, but the Anglicisations are ill-judged and distracting. Too many "franklins", and goodness only knows what possessed the translator to render Olaf as "Olave".