Death's Cathedral

When Shane Ryan was drawn into underground fighting that was going on between humans and ghosts he had no idea what he was truly getting involved in. But as the series continues, he is hunting Lazarus, trying to determine how he could absorb the ghosts, and grow stronger.
With a ghostly sidekick with a strange side, Shane searches for Lazarus but is tipped off about a town that was destroyed. Every person was killed by an invisible force, and Shane knows that somehow Lazarus is behind it.

Absolutely loved this book! It was amazing!