Feiwel&Friends All Is Fair - Dee Garretson

Lady Mina Tretheway knows she's destined for greater things than her fancy boarding school, where she's being taught to be a proper English lady. It's 1918, and war is raging across Europe. Unlike her father and brother, who are able to assist in the war effort, Mina is stuck sorting out which fork should be used with which dinner course. When Mina receives a telegram that's written in code, she finally has her chance to do something big. She returns to her childhood home of Hallington Manor, joined by a family friend, Lord Andrew Graham, and a dashing and mysterious young American, Lucas. The three of them must band together to work on a dangerous project that could turn the tide of the war. Thrilled that she gets to contribute to the war effort at least, Mina jumps headfirst into the world of cryptic messages, spycraft, and international intrigue. She, Lucas, and Andrew have to work quickly, because if they don't succeed, more soldiers will disappear into the darkness of war.