A Strange Disappearance

A young woman has disappeared from a fifth avenue home in New York. The bachelor owner, Mr Holman Blake, says he knows nothing of her. But the housekeeper Mrs Daniel is worried and goes to the police. Investigator Q finds blood on the windowsill and the woman has not taken the time to pack. It seems that she left unwillingly. But why leaving from the roof when she could have used the servant door?