One Cold, Dark Night (Star Elite Norfolk #4)
Rebecca King

A mysterious woman in black who floats around Winterley Hall convinces Ezra that Elspeth's life is in danger. However, lost amongst the dark halls of Winterley as he is, Ezra finds it impossible to identify where danger lurks. His investigation into Winterley's secrets swiftly becomes complex and even more dangerous when the figure in black makes it clear that Ezra's the next target.
Can he identify the intruders stalking the halls of Winterley, watching the women sleeping in their beds at night? More importantly, can he keep Elspeth out of the intruder's clutches long enough to discover all her secrets, and is Elspeth the one Ezra should fear the most?