The verdant hills and valleys of Central New South Wales, Australia, provides the awesome setting for this adventure of three capable children who volunteer to ride the boundary line of their property in order to check the area. Jane, Bobby and cousin Vincent estimate the ""mission"" will take at least a week. When they are finished in four days, they decide to use the remainder of the time to explore the region of World's End Falls. Though cousin Vincent shines as the hero in the routine part of the journey, it is young Bobby who saves the group in a time of crisis. Where Vincent's conservatism prevents him from exercising ingenuity, Bobby's newly discovered leadership ability allows him to encourage his companions when they become hopelessly lost in the desolate hills. After one painful night in the open, Bobby finds a cave and coincidentally frees a trapped sheep dog who leads the children to the safety of a farmhouse. Aside from their eventual rescue, the last part of the story is a superfluous segment to an excellent picture of three children at the mercy of an isolated terrain. The full majesty of the country comes through and for this alone the book is rewarding.