When Buckingham Palace announce that the Queen's exotic animals will be moved from London Zoo to the Tower of London, Beefeater Balthazar Jones, owner of the world's oldest tortoise and collector of rare raindrops, is charged with minding them. The magical (and ghostly), labyrinthine world of the Tower is already home and workplace to a strange collection of creatures - including the Reverend Septimus Drew, the Ravenmaster, and Ruby Dore, landlady of the Rack & Ruin, and, of course, Jones and his wife, the spectacular and fiery Hebe. Once it was home too for Milo, their young son, but then came the fateful day that haunts them both.