It was enough to make anyone say "Hullo!" The incredible was visible to them all. The lamp hung upside down in the air, burning quietly with its flame pointing down. 

Mr. Fotheringay stood with a forefinger stretched out and the troubled face of one expecting a terrible crash.

the troubled face of one expecting a terrible crash怎么理解？of one =of a  person字面意思是一个人的烦恼表情？of介词是什么意思？关于吗？expecting a terrible crash修饰one。一个人生怕摔碎的烦恼表情？