'I Spy' is an adventure-mystery novel written by Natalie Sumner Lincoln. The story is set in World War I, when the allied forces, English and French, had been bent backward day by day, until it seemed as if Paris was fairly within the Germans' grasp. Bent indeed, but never broken, and with the turning of the tide the Allied line had rushed forward, and France breathed again. Two men, seated in a room of the United Service Club in London one gloomy afternoon in November, 1914, talked over the situation in tones too low to reach other ears. The older man, Sir Percival Hargraves, had been bemoaning the fact that England seemed honeycombed by the German Secret Service, and his nephew, John Hargraves, an officer in uniform, was attempting to reassure him. It was a farewell meeting, for the young officer was returning to the front.
Natalie Sumner Lincoln (4 october 1881 - 31 august 1935) was an American writer. She was born in Washington and spent her whole career in this town. She was editor of the D.A.R. Magazine (Daughters of American R) from to .
She wrote 10 crime mystery novels with Inspector Mitchell from the Washington Police Department (1916-1927), and 2 novels with Detective Ferguson in the same town (1920-1921).
In 1922, The Washington Times mentioned her as The Conan Doyle of Washington.