The Intriguers by William le Queux

Needless to say that Nada was very much alarmed by the threat which her brother had flung at her when she spoke of leaving the Palace. She tried to reason herself into the belief that her fears were groundless. In their not infrequent quarrels he had more than once threatened to lock her up in that gloomy castle in order to bring her to her senses.

But nothing had ever come of it. He was hotheaded and overbearing, but she did not believe him to be vindictive. Of course, in forming this lenient estimate of a character not to be very easily fathomed, she was grievously mistaken.