The Book of War - The Last Oracle

Helena and the oracular bookstore Abernathy's stopped an attack by the alien invaders' human allies and destroyed their attempt at a second oracle, giving the Wardens much-needed victories. Now, after months of fighting a defensive war, the Wardens plan a direct assault on the enemy stronghold. But as the battle approaches, Abernathy's has other plans. The oracle directs Helena to contact four ordinary people with extraordinary talents whose abilities will change the course of the war.
Convincing them to join the fight challenges Helena's persuasive powers to the extreme. If she fails, it will mean the deaths of thousands-including those Helena loves most.