"Well," Dimsdale leaned back, twisting his half-smoked cigar between his fingers. "It was the masked ball--this silly form of entertainment, which Ida insists upon having for her birthday--which gave me the idea. You see, with the chance of being masked and mingling amongst my guests, The Spider will be the more ready to come, and will suspect nothing. I am writing to him to-morrow, telling him about this ball, and am suggesting that he should come wearing a mask to enjoy it. Then, at eleven o'clock, say, he can secretly meet me in this room to receive the money." "Cash?" echoed Vernon significantly. "Of course. The fellow's too clever to risk cheques. They would put the police on his track; would put the police on his track, my boy." "But do you intend to pay the money?" "No, no, no, no! How stupid you are, Arthur. Use your brains, use your brains, boy. I shall offer to pay the money, and then you, concealed behind the screen--that Japanese one up in the corner--can rush out and----" "But I have no authority to arrest him," interrupted Vernon impatiently. "Why not post a policeman, or a plain-clothes detective, to catch the beast?" "I don't want any policeman in my house," retorted Dimsdale gruffly; "and you are detective enough for me. If he blackmails me, you will be the witness, and we will have every right to hold him. Then you can take him away and hand him over to the Hampstead police." "He may show fight." "Then have a revolver with you," snapped the old man. "I don't want a scandal and a row on Ida's birthday, and in my house." "It seems to me that you are going the best way to have one," said Vernon deliberately; "much better let me inform the police and have the thing done in an orderly fashion." "No, I tell you." Dimsdale again slapped the table. "I'll do it my own way or not at all. If I catch the beast by laying this trap, both myself and Mrs. Bedge and many other people will be safe. But if we call in the police, however secretly, The Spider--who seems to have ears and eyes all over him--will get wind of the ambush." Vernon nodded. "There's something in that," he assented. "Perhaps on those grounds it will be better that we should engineer the job together. Well," he stood up straight and slim, "I shall come here on the night of the ball--by the way, when does it take place?" "Monday week. It's a short notice, but Ida only thought yesterday of this way to celebrate her birthday." "Are you quite sure," asked Vernon, taking up his tall hat, "that it is advisable to lay this trap on the night of the ball?" "Yes, I do; yes, I do," said Dimsdale in a fussy manner. "The mere idea of masks, which will enable the scoundrel to hide his infernal face without comment, will recommend itself to him. He will think that he is exceptionally safe, not dreaming that I intend to fight." "You will fight, then?"