Why should she be in danger at all, from any member of the Triangle? What did she know, or what had she had the chance of deducing, which might imperil the secret of the Apex? Here at least she had a little knowledge to train on the question. She knew some people who were connected with the mystery: Lord Hannassay, Mattock, Raegenssen, and--Uncle Joe. The inclusion of her uncle amused her; but she left him in the list because he had received one of the Triangle cards. Now, what did she know about each? She took them one by one. Lord Hannassay? The Triangle had murdered him. She knew little about him, except that he held a minor position in the Home Office. Was he connected with any of the other three? ... The recollection of his interest in Mattock, to which Storm had attached some import, came to her in a flash. She wrestled with the circumstances of that case. Mattock had been Hannassay's secretary, and had forged his employer's name to a cheque; Hannassay had prosecuted him without mercy, and Mattock had gone to prison. Therefore Mattock had a grudge against Hannassay. Then how did the others fit in? She was certain that Raegenssen belonged somewhere in that complicated jig-saw--she had a distinct recollection of the afternoon when the Hirondel had skidded into him. Raegenssen had been knocked half unconscious, and she had heard him speak as he was coming round: if he had been partially stunned, his brain would have functioned without the restraint which his caution imposed upon it in ordinary life, and he might have let fall a hint of Something. And that Something had had an astounding effect on Storm, Mattock, and Uncle Joe. She could even picture their different expressions--Storm's tense inscrutability, Mattock's passion, and Uncle Joe's excitement. What was it Raegenssen had mumbled? Some girl's name ... _Sylvia_! That was it. Then where did Sylvia come in, and who was Sylvia--why should she have such an incredible influence upon three men brought together practically by a fluke? Another idea came tapping at Susan's brain. She could not quite place it--it was something which hammered at the doors of her conscious mind and yet just missed gaining ingress. A cold wind seemed suddenly to lap her spine, sending a shiver up her back to the nape of her neck. She had a numbing sensation of being on the verge of a bottomless precipice, of being on the threshold of some terrible realisation. There was something enormously significant attached to that name, and yet it was only a superficial association. It wasn't the name itself, but ... but ... but the way it was said--Raegenssen's voice!