Dan Jolley 
Five Elements: The Shadow City [EPUB ebook] 

The second book in an epic middle grade series with awesome elemental powers, nightmarish creatures, and nonstop adventure that will thrill kids who love Avatar: The Last Airbender,  Rick Riordan, and Brandon Mull.Five elements. Two worlds. One city…and one chance to save it.In the past two weeks, Gabe Conway has fought a six-winged dragon, bound himself to the element of fire, and rescued one of his best friends from the twisted parallel dimension known as Arcadia. Now he has to find a way to do something even more impossible: destroy Arcadia forever—before a sinister cult unleashes its nightmare of death and destruction across San Francisco.“Thrilling entertainment. This fast-paced fantasy adventure should please readers of Cassandra Clare and Holly Black’s Magisterium series.”—School Library Journal