Each morning, the Professor and the Housekeeper are introduced to one another. The Professor may not remember what he had for breakfast, but his mind is still alive with elegant mathematical equations from the past. He devises clever maths riddles - based on her shoe size or her birthday - and the numbers reveal a sheltering and poetic world to both the Housekeeper and her ten-year-old son. With each new equation, the three lost souls forge an affection more mysterious than imaginary numbers, and a bond that runs deeper than memory.