John Dee was the most famous scientist of the Elizabethan age. A great mathematician, he introduced Euclid to Englishmen; a brilliant cartographer, he was the guiding spirit behind the sea journeys undertaken by Chancellor, Frobisher and Hawkins; and he invented the concept of the British Empire. His library at Mortlake was the largest in England and Queen Elizabeth I called him ‘my philosopher’. Consulted by princes and emperors throughout Europe, he declined the post of philosopher at the Muscovite court, which would have paid £2,000 a year. But by the end of his life his star had fallen; he was hounded from the Continent and ended up back in Mortlake, living in poverty. He died aged eighty–one, his name besmirched, his books plundered. His crime? Dabbling in magic.