The error was not only natural, it was inevitable. It was no case for hesitation nor even for rapid decision; but even had such a necessity arisen in Mr. Bevan's mind, his habit of prompt decision would have saved him from even a moment's delay. He had found his quarry and he would hunt it down. With the sober walk that denotes a man of the world, but now and then twirling his umbrella as though his birth and status gave him a right to despise convention, nay, going once or twice so far as to whistle the bar of a tune, Zachary proceeded northward to the Tube, and turned into that station which takes its name from Bond Street. The Tubes of London have added yet another problem to the already arduous intellectual task of that great army of detectives which stands between Society and Anarchy. To follow a man in the street, to pursue his cab or his omnibus at the regulation distance advised by Captain Wattlebury, M. Grignan, and other authorities of European reputation, is an easy matter; but once let your man get into the train ahead of you on the Tube, and you have lost him! The Tube necessitates, as all my readers who have engaged in detective work will recognise, a close proximity to the person watched; but Mr. Bevan was equal to the occasion. Fully appreciating the strategical advantage of the stairs, he was at their foot long before the lift had reached the level of the trains, and following Zachary's tall hat through the crush, he sat down in the carriage next to that in which the scent lay, gazing into vacancy and sucking the top of his umbrella. Mr. Bevan watched him narrowly through a contrivance with which all the forces of law and order are familiar: a little book which can be easily held before the face as though one were reading, but which is pierced by a convenient hole through which the right eye can sweep the landscape beyond. Zachary changed for Hampstead, and so did Mr. Bevan. At the junction he bought a newspaper, the name of which Mr. Bevan, to his great chagrin, was unable to note, as he folded it inside-out and read the lower half of the sheet. At Hampstead, I find it in Mr. Bevan's notes that they alit, and they reached the happy upper world together. Zachary made straight for the Heath. Mr. Bevan, now free to follow him at a discreet distance, did so, but grew fainter and weaker as he walked, for he was in desperate need of food. He hoped and prayed that the chase would turn into a restaurant: his prayer was answered, though in a manner shocking to one who still maintained his respect for rank. Zachary turned into a little public-house of an unpleasing type, nodded cheerfully to the potman, whom he addressed as "Larky," and ordered--of all things in the world--gin and water!