A Poor Wise Man by Mary Roberts Rinehart

Set in the early 1920s, A POOR WISE MAN follows Lily Cardew, a romantic young woman rebelling against her autocratic and conservative steel magnate grandfather. Cardew's service in the Red Cross during the war has opened up new horizons to her--she's been exposed to new ideas and people with radically different backgrounds and upbringings. In a quintessential act of rebellion, she becomes involved with a Bolshevik revolutionary.