The British, realising how serious a situation might arise should De Wet succeed in penetrating the Colony and in joining Hertzog and Kritzinger, made every effort both to head him off and to bar his return.  General Lyttelton at Naauwpoort directed the operations, and the possession of the railway line enabled him to concentrate his columns rapidly at the point of danger.  On February 11th De Wet forded the Orange River at Zand Drift, and found himself once more upon British territory.  Lyttelton’s plan of campaign appears to have been to allow De Wet to come some distance south, and then to hold him in front by De Lisle’s force, while a number of small mobile columns under Plumer, Crabbe, Henniker, Bethune, Haig, and Thorneycroft should shepherd him behind.  On crossing, De Wet at once moved westwards, where, upon February 12th, Plumer’s column, consisting of the Queensland Mounted Infantry, the Imperial Bushmen, and part of the King’s Dragoon Guards, came into touch with his rearguard.  All day upon the 13th and 14th, amid terrific rain, Plumer’s hardy troopers followed close upon the enemy, gleaning a few ammunition wagons, a maxim, and some prisoners.  The invaders crossed the railway line near Houtnek, to the north of De Aar, in the early hours of the 15th, moving upon a front of six or eight miles.  Two armoured trains from the north and the south closed in upon him as he passed, Plumer still thundered in his rear, and a small column under Crabbe came pressing from the south.  This sturdy Colonel of Grenadiers had already been wounded four times in the war, so that he might be excused if he felt some personal as well as patriotic reasons for pushing a relentless pursuit.  On crossing the railroad De Wet turned furiously upon his pursuers, and, taking an excellent position upon a line of kopjes rising out of the huge expanse of the Karoo, he fought a stubborn rearguard action in order to give time for his convoy to get ahead.  He was hustled off the hills, however, the Australian Bushmen with great dash carrying the central kopje, and the guns driving the invaders to the westward.  Leaving all his wagons and his reserve ammunition behind him, the guerilla chief struck north-west, moving with great swiftness, but never succeeding in shaking off Plumer’s pursuit.  The weather continued, however, to be atrocious, rain and hail falling with such violence that the horses could hardly be induced to face it.  For a week the two sodden, sleepless, mud-splashed little armies swept onwards over the Karoo.  De Wet passed northwards through Strydenburg, past Hopetown, and so to the Orange River, which was found to be too swollen with the rains to permit of his crossing.  Here upon the 23rd, after a march of forty-five miles on end, Plumer ran into him once more, and captured with very little fighting a fifteen-pounder, a pom-pom, and close on to a hundred prisoners.  Slipping away to the east, De Wet upon February 24th crossed the railroad again between