The Box Office Murders by Freeman Wills Crofts

French's conversation with Molly Moran had given that young lady very seriously to think. From the beginning she had realized that the undertaking in which she was assisting was unlawful, if not actually criminal. She was not making a bid for French's sympathy when she told him that since she had become involved she had been miserable and in terror. This was the literal truth. Continually she had felt as if she were living on the edge of a volcano which might break out and overwhelm her at any moment. Visions of dismissal, of imprisonment, of ruin were constantly before her and in spite of the money she was earning she would have been thankful if she could have given up the whole thing and removed its evil shadow from her life.

But never in her wildest imaginings had she conceived that the affair could be weighted with murder or she herself in actual physical danger. The story of Thurza Darke and her two predecessors had therefore come to her as an appalling shock. Indeed, she realized that had it come alone she might easily have been driven by panic to take some step which might have precipitated the very crisis she feared.