"Then it's going to be an extra specially high one," remarked the experienced Gabrielle, looking down at the surging, bankless Mentle. "I should think they would get some healthy splashes in the field; the spray comes right over the old sea-wall in a really rough tide." "Oh, never mind the old tide--let's get on to Mote!" urged Joey. And just as she said it, the thing happened. There was a sudden appalling roar--a long, crashing roar. The river gave a sort of shuddering sigh, and then, far off along its brimming level, something seemed to rise up--a great grey wall, foam-tipped. Joey stared at it, fascinated, but not frightened. But Gabrielle knew the fens. She grasped Joey roughly by the arm, Gabrielle, who was always so gentle in her ways. "Come on! Run! Run back from the river," she screamed. "That's an Eigre!" Joey hadn't a notion what an Eigre might be, but there was urgency in Gabrielle's tone. They all three turned and ran back along the road that they had come. Only Joey looked over her shoulder, and thought she never would forget what she saw as long as she lived. The wall of water, curling as it came, swept nearer; then suddenly it broke with a noise like thunder, and, with a great swirl and rush, the water was over the bridge in a whirl, was spreading far and wide, was about their feet. "_Run!_" Gabrielle shouted again, as a second great surge brought the water washing against their knees. And run they did, through a world that seemed all water, as far as the eye could reach. No one who was at Redlands then, least of all those three friends, will ever forget that wild 31st of October, when the old sea-wall went down, and the highest tide that men had known for thirty years burst in upon the Deeps of Little Holland! CHAPTER XXI IN THE ROUND TOWER There are white posts set at intervals along the fen roads to guide travellers in the dark. A necessary precaution as the roads are often ditch-bordered, and for half the year those ditches brim. The posts are barely two feet in height; by the time the girls had reached the spot where John had left them, only the tops of those posts were left uncovered; the tide was plainly driving in with terrific force, and wherever they looked they saw nothing but the waste of tossing water. Not one of the three would have owned to being frightened, and it was in quite a cheerful voice that Noreen put their worst danger into words. "Hurry up, you two. We must get somewhere before the posts cover, or we shan't be able to find the road."