A Small Gray Dot

It is the year 2047 and twenty-five-years-old Tennessee Murray has realized his ambition to teach and his dream of publishing a book. He is preparing to marry the love of his life and things couldn't be better. Then one morning he steps out into foggy weather and finds the world has taken a turn for the extremely bad. In a matter of minutes, half the population of Earth dies in a horrible fashion.
It's not an ultimate war or biological disaster, and no oversized meteorite hit the planet or any other such catastrophe. It is sudden, it is deadly, and it is inexplicable. Seven and a half years later, Tennessee, now a tracker in a diminished world that is limping along, sets out to find a missing young woman and makes a discovery that sheds light on the longstanding mystery. He also learns that a finale is in store for the remaining peoples of Earth.
Could the fate of the world hinge on the actions of an ex-middle school English teacher?