The Fifth Wave  by Rick Yancey is the new IT title. Get on the hold list now before it explodes and keep your eye out for Lucky Day copies. I started the title last night and could barely put it down to sleep. Cassie is alone, totally alone. In this sci fi alien invasion novel, Cassie must do the unthinkable - trust - in order to save her brother! Goodreads describes the book as "The Passage  Meets Ender's Game ."
From the book:
"After the 1st wave, only darkness remains. After the 2nd, only the lucky escape. And after the 3rd, only the unlucky survive. After the 4th wave, only one rule applies: trust no one."