Sukey and Chris are now much better riders, but no better at dealing with the ghastly Jess, who has a pony of her own.

Angela is back too, and she hears a horse neighing on a cargo boat. Then Jess sees a horse being unloaded from the boat at the dead of night. Sukey and the others are convinced this is suspicious, and when they learn a famous stallion has been kidnapped they start to wonder if there's a link to the mystery horse.

Does the mysterious Mr Spalding, who's just moved to the moor to start a stud, have anything to do with the mystery horse? Or is there an innocent explanation? The moors children are determined to find out.