Without warning or provocation, a Xindi weapon appears above Earth and unleashes a blast that kills millions across two continents. It is only the first such weapon: a second is being built, and this time it might very well destroy the entire planet. Desperately trying to save the Earth and her people, Starfleet must, in a heartbeat, change its mission from one of peaceful scientific exploration to one of military service.

There is only one ship fast enough to stop construction of this new weapon: the Starship Enterprise. But its crew can't do it alone. Captain Jonathan Archer accepts aboard his ship a contingent of Military Assault Command Operations personnel: battle-hardened soldiers known as MACOs.

Starfleet and the MACOs are two different services now sharing a common goal, but they are divided as to how to reach it. It is a culture clash that echoes across the centuries of military service. The men and women now aboard Enterprise know they must succeed in working together or the price will be paid in the blood of innocents. Failure is not an option.