Missy, formerly the master, escaped from Gallifrey when the Doctors freed the planet from the Time War in The Day of The Doctor. Now, only she knows its whereabouts. But as she watched the Doctor and Clara on their adventures through season 8, she left a vital clue to its whereabouts somewhere in space and time and one of the doctors enemies has found it. Can you figure out what the clue is, where she left it and who holds the key to locating Gallifrey and sending the doctor home?