When their father is reported missing at the front during World War I, Jane and Katherine are stamped and sent by parcel post across the country to their Aunt Lucille Forrest in New Jersey. The two girls manage to smuggle their dog into the mail bag as well. Aunt Lucille is in love with Lt. Tom Hayes, but she is angry with him after he resigns his commission at the start of the war. She does not know that Tom is in the Secret Service, and she becomes jealous of a female spy whom Tom is trailing. Jane and Katherine's mischievous pranks finally assist in capturing the spy and the secret plans, and getting Aunt Lucille back together with Tom.