Young Daisy and her six brothers and sisters love Hartslove, the crumbling castle that has been in their family for hundreds of years. But their kind but feckless father, scarred by his experiences in the Crimean War, and by his wife's desertion, is drinking the family money away. Then he puts Hartslove up for sale: he has spent his remaining money on a young, wild, horse. Daisy, passionate about her home and her family, is determined that the horse is the One; that he will win the Derby and save them all.

But not everyone at Hartslove is on Daisy's side, and rich people are descending on the castle every day with an eye on snapping it up for themselves. With only months to go before the Derby, can Daisy and her wild brother Garth overcome the odds and lead The One to glory?