The Cleansing (Earth Haven: Book 1) - Earth Haven, #1

Apocalypse unleashed. Swift and deadly. Merciless. Seven billion people inhabit this planet in blissful ignorance of imminent annihilation. Destruction comes, not from meteors or nuclear holocaust, but from a source no one even knows exists. The architects of doom have long moved among us, hidden in plain sight, waiting for the signal to trigger our extinction. A handful of survivors, traumatised and bewildered, must come to terms with the new reality.
And quickly. For the Cleansing is only the beginning.