The Red Signal by Grace Livingston Hill
The Red Signal is a mind-bending romance written by Grace Livingston Hill.
This love story is about the heroin -- Hilda Lessing and her adventures foiling German spies set against a World War I backdrop. And how she escaped from the kidnapped of the enemies with the help of her hero -- Daniel Stevens.
"When David Stevens, engineer on Freight No. 5, snatched Hilda Lessng from the path of a fast express, he did not know that there was the making of a heroine in her slender frame, nor that fate was to entangle this simple child with himself in a web of plots and danger, from which she was to rescue them at the risk of her life. But some of the most breath-taking adventures of all fiction lie between the consummation of her happiness and the foiling of a diabolical plot threatening the safety of the nation."