Topher's cat, Ka, is not always who she seems to be. Sometimes she disappears for days and all that Ka has left by his bedside is a little stone carving of a cat. One days Ka leaves a clue on Topher's computer. She types Bubastis and soon Topher finds himself time-travelling to Ancient Egypt where Ka is in terrible danger.

Ka, the time-traveling cat, has gone back to Tudor England and Topher needs Doctor Dee to help find her. But Doctor Dee is busy searching for something far more important—The Philosopher's Stone.

Topher Hope is on the move again. When his devoted cat, Ka, leaves a mysterious clue on his computer, a Roman word—CA;;LLevA—he follows her to a Romano-British settlement in AD 79. Ka is happy among the cat-adoring conquerors and their central heating! Topher, now a British boy apprenticed to a Roman mosaic maker, has mixed loyalties. When the eagle, symbol of Roman power, disappears from the forum, the fragile peace is threatened and Topher begins a desperate search. Can he find it and save his Roman friend, Marcus, from the Druid's murderous sickle? In this adventure, Topher needs all the amazing powers of the time-traveling cat.

Topher Hope is distraught when Ka, his devoted cat disappears, leaving only one word on his computer as a clue: TENOCHTITLAN. Topher is horrified. To save Ka, he must travel back in time to the home of the blood-thirsty Aztecs. Along the way, Topher befriends Pima, an Aztec girl doomed to be a sacrifice to the gods. In this fast-paced adventure, Topher races against the clock to save Pima and Ka from terrible danger.

Topher is planning a trip to London to visit his friend Ellie—but will it be safe with all the terrorist threats? It worries him, and so do the extended absences of his beloved cat, Ka. She is going traveling again, and Topher doesn't want to lose her. Sure enough, in the middle of a big bomb alert, Topher is called away—to a Saxon village threatened by Norsemen. Now he must get the villagers to heed his warning and foil the aggressors led by a terrifying Viking infamous for his cruelty and devious tricks.

A Victorian mystery for the time-travelers—Topher and his amazing cat—to resolve Topher's cat, Ka, has time-traveled again, leaving him the clue "CAppeLLis." Following her, Topher finds himself in Victorian London where disease is rife and the Thames is clogged with stinking sewage. Topher discovers a plot to kill Joseph Bazalgette, the man who is trying to save the city. Determined to foil it, Topher must first escape from an arch-criminal and his den of thieves. This well-researched and exciting adventure is a great read for Doctor Who fans.