"This blackguard from the first kept the figure, the personality, of Frank Errington before his mind. Frank Errington was the dust which the scoundrel threw metaphorically in the eyes of the police, and you must admit that he succeeded in blinding them--to the extent even of making them entirely forget the one simple little sentence, overheard by Mr. Andrew Campbell, and which was, of course, the clue to the whole thing--the only slip the cunning rogue made--'_Au revoir_! Don't be late to-night.' Mrs. Hazeldene was going that night to the opera with her husband-- "You are astonished?" he added with a shrug of the shoulders, "you do not see the tragedy yet, as I have seen it before me all along. The frivolous young wife, the flirtation with the friend?--all a blind, all pretence. I took the trouble which the police should have taken immediately, of finding out something about the finances of the Hazeldene _ménage_. Money is in nine cases out of ten the keynote to a crime. "I found that the will of Mary Beatrice Hazeldene had been proved by the husband, her sole executor, the estate being sworn at £15,000. I found out, moreover, that Mr. Edward Sholto Hazeldene was a poor shipper's clerk when he married the daughter of a wealthy builder in Kensington--and then I made note of the fact that the disconsolate widower had allowed his beard to grow since the death of his wife. "There's no doubt that he was a clever rogue," added the strange creature, leaning excitedly over the table, and peering into Polly's face. "Do you know how that deadly poison was injected into the poor woman's system? By the simplest of all means, one known to every scoundrel in Southern Europe. A ring--yes! a ring, which has a tiny hollow needle capable of holding a sufficient quantity of prussic acid to have killed two persons instead of one. The man in the tweed suit shook hands with his fair companion--probably she hardly felt the prick, not sufficiently in any case to make her utter a scream. And, mind you, the scoundrel had every facility, through his friendship with Mr. Errington, of procuring what poison he required, not to mention his friend's visiting card. We cannot gauge how many months ago he began to try and copy Frank Errington in his style of dress, the cut of his moustache, his general appearance, making the change probably so gradual, that no one in his own _entourage_ would notice it. He selected for his model a man his own height and build, with the same coloured hair." "But there was the terrible risk of being identified by his fellow-traveller in the Underground," suggested Polly.