The King of Plagues brings back some baddies from a prior book as the Department of Military Sciences discovers the existence of the Seven Kings. They are a powerful cabal bent on causing chaos throughout the world and profiting from it. The Seven Kings use their knowledge of the upcoming chaos they will cause to make money on various fronts as wars and catastrophes impact the world markets. Ruled over by "The Goddess" there are seven members of the cabal each with an advisor who acts as their "conscience." It turns out that they have a vacancy and are in need of a new King of Plagues.

The DMS lost a major member at the end of The Dragon Factory and the impact of that loss is evident as Joe Ledger is still on a leave of absence when this one starts.  Joe is grief stricken and trying to find a way to cope with yet another loss in his life and he has been off active duty for a while. Of course a new threat causes Mr Church to coax Joe back into action and when he returns Joe brings along a new companion, Ghost. Ghost is a white German Shepard who is trained in many capacities including bomb sniffing and combat. Ghost is also an excellent judge of character and plays a key role as Joe's new partner. Echo team also has also added some new members while Joe was gone, including John Smith, the best sniper in the world. John's code name is Chatterbox, since he barely talks at all, but when he brings down the Hammer of God on someone he never misses. Circe O'Tree is another new character introduced who brings her skill set over to the DMS as a terrorism expert.

A terrorist attack in a London hospital kicks things off as the Seven Kings start to implement a new wave of chaos involving their new King of Plagues. By coercing individuals that work in key locations around the world the Seven Kings are recreating a modern version of the Ten Plagues from the Bible. These attacks are perpetrated by ordinary people in vital roles at these key locations and this combined with social media manipulation from The Goddess starts to position the Seven Kings as a powerful force to be reckoned with. However, another rival cabal starts feeding information on the activities of the Seven Kings to the DMS and Joe and team find themselves caught between a rock and a hard place. It starts to become obvious that the DMS is being used as a tool for one rival to take down another but they can't ignore the threats being orchestrated by the Seven Kings and they must stop them at all costs.

Now that the bad guys are starting to have a story arc of their own the series is gathering some momentum as key players on various points of the moral compass vie to gain the upper hand. Mr. Church and Aunt Sally, the two key leaders of the DMS, clearly have a nebulous past of their own and every bad guy that shows up knows about them and fears what they are capable of. This adds a nice layer to the overall series and makes it more engaging than just Joe Ledger and Echo team going around shooting people.

Ray Porter delivers another excellent narration for the audiobook and I continue to march forward in the series. It isn't the greatest series ever but it is entertaining and a nice change of pace within the genre. I do enjoy the random pop culture references made throughout each book and often chuckle when Ledger compares things in his "real world" to other fictional worlds.