In the midst of a World War, the true enemy was unseen.

It came with a handshake or a breath and it left behind 40 million dead.

In October 1918, World War I was winding down, but the world had yet to face the deadliest killer known. Spanish Flu would devastate the world.

In Cumberland, Maryland, Dr. Alan Keener, a young doctor fresh from medical school, suspects the flu has reached Allegany County. He wants to take steps to prevent its spread, but he is met with resistance from old-school doctors who believe that the flu’s deadliness is overblown and easily treated.

They soon learn differently as the flu begins to spread throughout the county. No one is safe from its effects.

A street preacher named Kolas aids the flu’s spread. During the delirium caused with his own bout with the flu, he believes he was anointed as the wrath of God and must spread to the flu to bring God’s retribution on the world.

As Alan races along with other doctors trying to find some vaccine that works, he must deal with overwhelming sickness in the county. Nearly half of the residents have the flu and many are dying. Nurses and doctors are already in short supply because many are serv-ing in the war. It becomes a critical shortage now as many fall sick with the flu themselves and those left have a workload that would be overwhelming even if there had been no shortage.

The fight becomes personal for Alan as his daughter and then his wife fall victim to the flu. Can he find a treatment to keep them alive or will they become one of the millions who are dying?