The 5th Wave

by Rick Yancey
Lexile:  690
Genre:  Science Fiction

Cassie and Sam are living happily with their parents.  And then the world ends and 7 billion people are dead.  Cassie thinks it is quite possible that she is the last human being on Earth.  She has survived the first four waves...but has no idea what the 5th wave will be and when it will happen.  All she knows is that she made a promise to her little brother that she would come and get him just as soon as she could.  Is Sam still alive?  And if so, can she find him before the 5th wave comes?