[3] After Roosevelt takes office, the United States conquers Mexico "for its own good" and begins a rigorous progress agenda.

[3] Luz O'Malley Aróstegui is a senior field operative for the Black Chamber, a U.S. spy and security agency.

Luz, who is ethnically Cuban-Irish, impersonates a Mexican-Irish revolutionary in order to contact a German agent who she learns is Baron Horst von Dückler.

They become lovers and Luz learns that the weapon, called "The Breath of Loki", is a poisonous gas that kills on contact.

[3][5] Eventually, Luz has to deal with a German plan to keep the United States out of the war by bringing the poisonous gas to the East Coast.