Nia, the middle girl in a large Welsh family, discovers her own special artistic talent as she uncovers the dark secret shared by the Llewelyn and Griffiths families.

While spending the summer in Tenby, Wales, with their grandfather, American cousins Zoé and Ian assemble an old glass puzzle, inadvertently unleashing ancient forces that threaten the island and allowing them to travel into the past.

Surely a peaceful holiday in the Welsh mountains will keep the children out of trouble. But the mystery of a rumbling mountain soon has them thirsty for more adventure. Philip, Dinah, Lucy-Ann, Jack, and Kiki the parrot are determined to explore the mountain and uncover its secret, but first they must escape from a pack of ravenous wolves and a mad genius who plans to rule the world.

In 1939 Wales, a strawberry roan Welsh pony named Lily and her rider Gwen are Pony Club members who enjoy competing in gymkhana games, but the start of World War II brings changes to their routine and a new member to the Pony Club--a prickly girl named Bridget, sent to the country to escape the threat of bombings in London.