Fairy Tail Volume 18 by Hiro Mashima
The battle between Fairy Tail's alliance of guilds and the Oracion Seis continues as the Nirvana magic activates. Nirvana was designed a long time ago to turn darkly-motivated wizards to the light, but it also functions in the opposite way, i.e. turning light-minded wizards evil. The promise of a lot of chaotic mayhem doesn't quite play out in this issue; even so, the story and battles are interesting. Helping the story is the return of Jellal (the villain from the Tower of Heaven story arc), whose amnesia causes interesting complications. The fight doesn't quite finish in this volume but things are finally going in favor of Fairy Tail.
Recommended, though at this point readers definitely can't jump in without reading several, if not all, of the previous volumes.