I've recently reviewed other books in the Kare Kids series, and now I have a chance to review book #4, The Travel Twins and the Lost Secret of the Vikings. Like the other books in the series, these are very family-friendly books that follow some independent kids solving problems.
This book takes place when the twins visit their uncle in Norway, where their uncle runs a museum who had a significant artifact stolen. On the hunt, the twins are kidnapped, and learn the reason the artifact was stolen - to try to recreate the Viking super-warriors.
The book is short enough that even slower readers can get through it easily, but there's enough in the book to keep avid readers moving quickly through the plot. The book is fun to read with a good level of suspense for middle elementary readers and has a satisfying ending.