This is a lively tale of adventure and courage, showing throughout the love of a boy for a horse. The author knows her terrain well, having spent much of her life in the Canadian province of Alberta. Bob and Elizabeth, brother and sister, with some assistance from neighbors and the Canadian Mounties foil the efforts of two horse thieves to steal, for a second time, Mystery, a thoroughbred. The story is solidly wholesome and packed with excitement, and ends happily when, through the generosity of the original owner, Mystery becomes Bob's own property. Should appeal to teen-agers who enjoy books about ranch life and horses.