Saving Arthur

Casey’s class is doing a play about King Arthur and the Knights of the Round Table. She is playing Guinevere. Casey takes her role very seriously, even borrowing a book from the library to learn more about the legend.
Casey’s mother owns an antique shop and when a grandfather clock is brought in one day, Casey offers to clean it up. She is surprised to discover the clock has no panels or joins, and growth rings indicate that it was carved from a single block of wood. She is even more surprised when she finds an old-fashioned key concealed at the base. What she doesn’t know yet is that the clock was carved from a tree enchanted by Merlin the magician.
After Casey’s discovery of the key, things change. The legend of King Arthur simply vanishes. Casey’s mother, teacher, and classmates know nothing about it. Casey’s copy of the play and the library book are now just blank pages.
Casey returns to the grandfather clock and discovers it is a time travel device when she is pulled through time by Merlin. Merlin tells her that six-year-old Arthur has recently drowned in a river. Casey needs to travel further back in time to save Arthur by altering the chain-of-events that led to his death.