Topher's amazing cat, Ka, has time-travelled again and left him yet another mysterious clue. Following his nose, Topher finds himself in Victorian London where disease is rife and the Thames is clogged with stinking sewage! There he discovers a plot to kill Joseph Bazalgette, the man who is trying to save the city. Determined to foil this foul plan, Topher must first escape from an arch-criminal and his den of thieves.