Ka, the time-travelling cat, has disappeared, leaving just one clue. Topher soon realises that she has gone back to Elizabethan England, and he fears that Ka is in terrible danger. Cats were tortured in Tudor England, so Topher must try to find her before it is too late. In doing so, he meets Queen Elizabeth and Doctor Dee, the court magician and astronomer, who thinks Ka can help him find the elusive Philosopher’s Stone.