The Mystery of the Swaying Curtains — Frances K. Judd

Kay's friend, Sissy Weller, unexpectedly learns that she is to inherit a fortune if she can prove that her real name is Christine Cleveland. The mystery is how anybody could connect Sissy with Christine when Sissy is adopted and has no knowledge of her true identity. After hearing additional details, Kay is convinced that Sissy is Christine, but how did the lawyer know? Kay learns that the lawyer received an anonymous letter telling him about Sissy, but who sent him the letter? How did that person know where Sissy is staying?

Kay investigates but is thwarted at every turn. The orphan home in which Sissy lived before her adoption has burned down. The one man who might know the answers to Sissy's past is missing.

Kay feels that someone is working to prevent Sissy from inheriting the fortune and tries to discover the truth before it is too late.