A disarmingly limpid telling of days spent training horses for the highest levels of competition, from newcomer Menino. What is it about riding and training horses that sustains the people so engaged? For that matter, what sustains the horses? Menino, a horse fancier of amateur status, visited extensively with three pairs of humans and beasts--Olympic-caliber duos--to get a sense of what makes them tick: Lendon Gray in dressage, the ``art for art's sake school of horsemanship''; Anne Kursinski, a leader in the world of show jumping, ``a glittering place layered with money and celebrity and artifice,'' and lately littered with the corpses of horses murdered for financial gain; and young Keith Taylor, pretender to combined training status, a form of competition that requires purity of movement, agility and maneuverability, and sheer speed. Menino is particularly interested in the everyday stuff, the nitty-gritty that gets things done and defines a way of life. She walks the courses with Gray, Kursinski, and Taylor, asks what they demand, takes measure of their various obstacles; spends time with each rider as he or she hustles for money to support an equestrian avocation. We read of farriers and of horse chiropractors and physical therapists. Perhaps most cannily, Menino speaks of horses: their independence and gameness, integrity and confidence. The author delves into horse behavior- -friendship and herding and consciousness and the ancient, fearful chimes that ring in a horse's mind when it falls: ``A horse that goes down is subject to predators and is powerless. Falling is frightening and humiliating. It is deathy.'' And her examination of horse-rider communication is as subtle as the imperceptible shifts of weight, the slight movement of reins that mean everything to those involved. Reading Menino is like taking a horse's muzzle into your hands, bending close, and breathing deeply. Sublime, with grassy notes.