The Clock Struck One by Fergus Hume

When Dora returned to the Red House, she made up her mind. Since Allen refused to tell her his secret, she would discover it herself, and judge if it were as serious a bar to their marriage as he asserted. She did not think for a moment that Allen knew who had killed Edermont, but she could not help concluding that he was aware of something likely to lead to the identification of the assassin. Perhaps he knew the story of Edermont's life, set forth in the manuscript which had been stolen from the bureau by the murderer. But whatever knowledge he was possessed of, Dora saw plainly enough that he was resolved to hold his peace. The truth is, she was afraid to admit his motive for silence even to herself. She half guessed the reason of his determination, but she neither spoke nor thought about it.

There were two ways in which she could go to work; either begin from the arrival of Lady Burville at Hernwood Hall, and progress onward to the committal of the crime, or begin from the fact of the murder, and trace back its motive to Lady Burville. After some consideration, she decided on the latter of these two courses. But Lady Burville had departed, and Dora was ignorant of her present address. Even if she did learn it, there was no excuse whereby she could gain an interview with the lady. She had no proof that this stranger was implicated in the crime, and if she were -- a fact which Dora fully believed -- there would be little chance of forcing her into confession. This course was therefore out of the question, but there remained the other.