An indispensable element in the series

It is a small book, a new, nothing comparable to the different volumes of the saga 'The Sword of Truth' (The sword of truth en). However, considering the price it is well worth the time, I would say it is essential.
This book was written just before 'Chainfire' and I read in this order, but history is independent and can be read at any time of the saga provided you have at least read the first volume .