Poppy Redfern and the Midnight Murders by Tessa Arlen

Poppy is the air-raid warden in her village of Little Buffenden and spends her evenings patrolling the area and making sure everyone is ready if the sirens go off. However, when two young women are murdered, she turns detective, questioning many in the village and teaming up with American pilot Griff O'Neal to discover the killer before anyone else comes to harm. Suspicions falls on the men who reside at the American air force base nearby, but Poppy believes the murderer is one of their own. This mystery is the first in the Poppy Redfern series.