The Boulsworths are expecting a foster kid but he runs away before he got there. Rocket went looking for him and soon learns the reason why he ran away and also the secret the foster kid is holding.
When a mythical Tancath is sighted in the woods, Rocket is determined to see the creature for himself. There he discovers Jade, a previous foster sibling, and learns that she has hitch-hiked back to the island.
When eccentric old Mary Mac's house is destroyed, she comes to stay at the Knot. Jade soon discovers that she is the ancient Queen of the Fairies, which could explain why the children's possessions have been disappearing.
When Rocket's sheep dog becomes sick in his old age, Rocket seeks out the ancient Wolf Tree, which is said to have the power to make the old young again.
When Rocket and Dibber find an old harmonica, the Oldest Man informs them that it belonged to the Lost Boy. Meanwhile, a mysterious new foster kid arrives at the Knot.
Everyone in the village thinks Brandon started the fire at school, so Rocket and Dibber decide to reform the Ballabungie Detective Agency and prove them wrong.