When Alfie and Angel Young arrive at Parkway Grange for the Easter holidays they are introduced to Mylor - a magnificent, unbelievable giant of a horse with a very special secret. For Mylor is an electronic miracle. A horse built by an eccentric Professor for the purpose of winning the English Grand National. Powered by the sun's rays and perfect down to the last detail, Mylor has ten times the strength of any living horse and a specially designed interior which allows him to be controlled by the children. An adventure crammed full of excitement soon follows, and as the story races towards its supercharged climax it is obvious that someone will stop at nothing in their efforts to destroy Mylor. Suddenly a new undreamed-of nightmare faces the children, and then everything depends on the instinct and love of The Most Powerful Horse in the World...