The Colonel, owner of Follyfoot, the Home of Rest for Horses, has been ill and has to go away to convalesce. Dora and Steve are left in charge, with the strict instruction, 'Don't buy any horses'. But when Dora sees the rangy, cream-coloured lame horse, Amigo, she is determined to save him from spending his last days pulling a heavy log-cart - even if it means borrowing money from sly Ron Stryker. But to pay Ron back, someone from Follyfoot must win the Moonlight Pony Steeplechase . . .
Follyfoot Farm is a retirement home for old or unwanted horses, invariably horses rescued from a cruel fate or cruel owners. It's run by the Colonel who is helped by his stepdaughter, Callie, and two stable-hands, Dora and Steve. These three youngsters have plenty to do at the stables, but can always find time to get involved in the mysteries and adventures that abound at Follyfoot.
Dora is invited out to America to help set up a home of rest for horses. When she leaves and is given a horse to take back to Follyfoot, she can't believe her luck. But once they're home things start to go badly wrong. One of the horses falls ill. And it looks like the same epidemic that is sweeping America . . . Has Dora's horse brought the disease to England?