Had Susan kept her eyes as open as usual during these expeditions to St. John's Wood, she would have observed, before this, that she herself was not the only person who was acting the detective round Dr. Duncan's house. On nearly every occasion that she had come to the neighbourhood, the shabby old woman had been there too, dogging her footsteps, watching her movements unsuspected, spying the spy. Susan had contrived to discover that Dr. Duncan was in the habit every Saturday of visiting a patient who lived a considerable way out of London. Failing, as I have said, with all her cleverness, to mature a definite plan of action, she determined to risk all, and call boldly on Mary while her husband was away on the following Saturday. She had a great confidence in her luck; she felt that something would turn up to favour her purpose, if she once gained admittance into the house. Knowing Mary as she did, she considered that it would not be difficult to terrify her again into her former crazed state. For a few days prior to her contemplated visit Susan was very fidgety; so to occupy her mind and prevent it from dwelling too anxiously on the perils of her task, she employed herself in a way which was peculiarly congenial and interesting to her. She set to work to forge as well as she was able--and she succeeded very fairly--a variety of documents; some purported to be letters from Catherine King, and other members of the late Secret Society; there were copies too of imaginary warrants for the arrest of unknown persons, whose appearance was carefully described. All these pointed to a great danger which threatened those who had been connected with the Sisterhood, especially Mary Duncan. There were other papers too which tended to show that the members of the Society attributed their peril to the treason of one of their number--clearly Mary--who was accused of having made certain disclosures to the authorities. They were alarming documents, intended to prove clearly that the young mother was suspected by both sides, was being hunted down by both the police and by her old associates. Susan would laugh to herself as she completed each of these works of art, and would look at them with no small pride. "I wonder if she will be fool enough to swallow all this?" she asked herself. "And yet why not? If she does believe in them, she will see that one course only is left to her--to fly from England, to desert her husband and her child, so as not to bring disgrace upon their heads. I believe I am on the right track at last. Ah! Susie, you have not forgotten your cunning after all!" At last the fatal Saturday arrived, and she started for St. John's Wood, armed with her papers, intending to show some, all, or none of them, to Mary, exactly as circumstances should make expedient.