Such was the news that greeted second-lieutenant Ralph Setley on disembarking at Boulogne. Bapaume and Péronne--places that for months and months had been practically within sight of the British trenches, and yet seemed as far remote as Peru. Miles and miles of deep concrete reinforced earthworks, hundreds of machine-guns, acres of formidable barbed wire, and the pick of the Kaiser's legions, had been in front of those two towns; and yet the Huns had gone--retreated. "A voluntary retirement, according to our plans." Ralph smiled when he read the mendacious German official report. Can any sane individual imagine a voluntary retirement in these circumstances. After two years of hard work, fortifying and defending those deep-dug trenches, would any belligerent voluntarily abandon ground gained and maintained at such a cost of blood and treasure? At a certain place, well behind the lines, Ralph was put through a hurried yet comprehensive "course" in Tank work. In company with half a dozen other young subalterns, he was under instruction from morning to night, with only brief intervals for meals. It would be difficult to find a squad more eager to grasp the intricacies of their future commands. They were, one and all, as "keen as mustard." Technical and practical work, intermixed with lectures on motors, machine-guns and quickfirers, hints on strategy and tactics, map-reading and dynamics--all were drummed into the active brains of the probationers, regardless of the adage, "A little knowledge is a dangerous thing." "Dangerous for the Boches, let's hope," remarked Danvers, a young second-lieutenant recently transferred from the Air Service, owing to a wound that rendered him unfit to fly, although his capacity in other directions was unimpaired. He had chummed up with Setley, and the two got on admirably. In private life Danvers had been a civil engineer, until the call of the sword took him from the plane-table and theodolite to the sterner profession of war. "I want to impress upon you fellows," said the major--who acted as instructor--"that you must not run away with the idea that landships are invulnerable." The class nodded their heads sagely. Considering most of them had seen derelict Tanks--in many cases showing huge rents in their armoured sides, caused by the impact of heavy shells--this announcement seemed superfluous.