But half an hour later, as he sat behind his little marble-topped table, smoking and sipping a liqueur, his eyes fell upon something across the square which brought him to his feet with a sudden exclamation.  One of the big electric trams that ply between the Place St. Germain des Pres and Clamart, by way of the Porte de Versailles and Vanves, was dragging its unwieldy bulk round the turn from the rue de Rennes into the boulevard.  He could see the sign-board along the imperiale—­“Clamart-St. Germain des Pres,” with “Issy” and “Vanves” in brackets between.

Ste. Marie clinked a franc upon the table and made off across the Place at a run.  Omnibuses from Batignolles and Menilmontant got in his way, fiacres tried to run him down, and a motor-car in a hurry pulled up just in time to save his life, but Ste. Marie ran on and caught the tram before it had completed the negotiation of the long curve and gathered speed for its dash down the boulevard.  He sprang upon the step, and the conductor reluctantly unfastened the chain to admit him.  So he climbed up to the top and seated himself, panting.  The dial high on the facade of the Gare Montparnasse said ten minutes to three.

He had no definite plan of action.  He had started off in this headlong fashion upon the spur of a moment’s impulse, and because he knew where the tram was going.  Now, embarked, he began to wonder if he was not a fool.  He knew every foot of the way to Clamart, for it was a favorite half-day’s excursion with him to ride there in this fashion, walk thence through the beautiful Meudon wood across to the river, and from Bellevue or Bas-Meudon take a Suresnes boat back into the city.  He knew, or thought he knew, just where lay the house, surrounded by garden and half-wild park, of which Olga Nilssen had told him; he had often wondered whose place it was as the tram rolled along the length of its high wall.  But he knew, also, that he could do nothing there, single-handed and without excuse or preparation.  He could not boldly ring the bell, demand speech with Mile.  Coira O’Hara, and ask her if she knew anything of the whereabouts of young Arthur Benham, whom a photographer had suspected of being in love with her.  He certainly could not do that.  And there seemed to be nothing else that—­Ste. Marie broke off this somewhat despondent course of reasoning with a sudden little voiceless cry.  For the first time it occurred to him to connect the house on the Clamart road and Mlle. Coira O’Hara and young Arthur Benham (it will be remembered that the man had not yet had time to arrange his suddenly acquired mass of evidence in logical order and to make deductions from it), for the first time he began to put two and two together.  Stewart had hidden away his nephew; this nephew was known to have been much enamoured of the girl Coira O’Hara; Coira O’Hara was said to be living—­with her father, probably—­in the house on the outskirts of Paris, where she was visited by Captain Stewart.  Was not the inference plain enough—­sufficiently reasonable?  It left, without doubt, many puzzling things to be explained—­perhaps too many; but Ste. Marie sat forward in his seat, his eyes gleaming, his face tense with excitement.