THE KEYS TO THE KINGDOM: SIR THURSDAY

This is the  4th book  in the series where it is about Arthur the boy we see in every book gets enrolled into the glorious army of the architect by accident to be trained as a high ranking soldier at the same time Arthur needs to find the 4th part of the will and claim the 4th key from sir Thursday who turns out to be the leader of the army Arthur
 has been enrolled in