J.M. Briggs 
The Iron Shadow [EPUB ebook] 

Alex’s priority is investigating the Tree of Reality regardless of Merlin and Morgana’s doubts. She knows that Arthur is also seeking information, but the question is why. With the Darkness looming and Arthur’s power growing, the mages have little time to find answers. Even worse, a new threat has entered the Iron Realm, which will test the Iron Soul as it has never been before.

Nicolas was not Morgana and Merlin’s ideal incarnation of the Iron Soul. So, they dealt with him. With a child Iron Soul now in their care and the population of Fae rising throughout Europe, the Grand Mages know it is only a matter of time before violence erupts. But a strange dancing plague and a new Fae leader calling himself Oberon was not something they could have ever predicted.