Lucy Wilson Mysteries: The Three Lucys

One day, Lucy Wilson wakes up and suddenly can't say the word 'I'. Its whole meaning starts to dissolve in her head, and soon, it spreads. She can't recall what day comes after Thursday. She doesn't know what that lesson with all the numbers is called. How soon before she loses the names of her own parents? Or her best friend, Hobo? From the world of Doctor Who.