For Polly, moving to Penhallow Hall is the fresh start she's been longing for since the death of her father. Her mum has got a job managing the stately home and once the last of the visitors leave for the day the place is all theirs! One night, Polly sleepwalks into the garden and wakes to find her hand on the head of one of the stone dogs that guard the steps down to the lawn. Then she feels him lick her cheek! The dog introduces himself as Rex, an Irish Wolfhound who lived at Penhallow many hundreds of years earlier. And he is not the only resident ghost - Polly has also glimpsed a strange boy around the place. With Rex's help she finds herself unravelling the story of his beloved master, William Penhallow, who was killed in the First World War aged only 17.

Polly and her new friends at Penhallow Hall wake Li-Mei, the Chinese porcelain dog from the Red Drawing Room. The little Pekingese tells them of her adventures with Sarah Penhallow – how they investigated rumours of smugglers and sighted a ghostly Green Lady down at the cove. Together, the friends set off to solve the mystery once and for all, and discover a secret tunnel. Here they come across a broken statue of a dog buried beneath a rockfall. Could their discovery have anything to do with the disappearance of Li-Mei’s canine companion?

At Penhallow Hall, where magical objects come to life, Polly and ghost hound Rex discover a toy dog on the nursery shelf. But to their surprise, this dog doesn't want to be woken! Polly finds out that the little toy dog was left behind at Penhallow during World War II by his evacuee owners, when the two children returned to the city. Polly invites her new friend at school, Lucy, over to tea and she seems strangely drawn to the toy dog, too. But before Polly can find out why, Lucy goes missing. Polly guesses where Lucy might be - but she'll need the little dog's help to find her.