A Mystery Under the Old Oak Tree

A young 'teenage' girl named Nara goes on an "adventure" with her younger sister that becomes all too real. She and her sister, Tilly, struggle to survive in a magical place called Lynisten until Marga, an old friend who she never really thought existed, appears to her and her sister. Marga helps Nara and Tilly get through dangers in Lynisten, but she seems to be keeping secrets from Nara. To what expense will Marga keep these secrets, and does Nara want to find out what they are?