Poppy McKeever is reluctant to move to an old cottage on Dartmoor - until she discovers that her new home comes complete with its own pony. But life at Riverdale is not as straight-forward as it seems, especially when Poppy spies a flash of white in the woods next to the cottage. Her stepmother Caroline is acting strangely and her adrenalin-junkie brother Charlie is on the hunt for big cats. But will Charlie's obsession drive the two children into dangerous territory? And when Poppy is faced with a terrible dilemma - to save her brother or the pony she has always longed for - who will she choose?