A young artist gets stranded in an extensive, immaculate forest in western Ireland, where, after finding shelter, she becomes trapped alongside three strangers, stalked by mysterious creatures each night.

The story of Vera Atkins, a crafty spy recruiter, and two of the first women she selects for Churchill's "secret army": Virginia Hall, a daring American undaunted by a disability and Noor Inayat Khan, a pacifist. These civilian women form an unlikely sisterhood while entangled in dangerous missions to turn the tide of the war.