>> harry potter. >> reporter: one might think the secret to selling books would be mimic harry potter's sourcery. or capitalize on "twilight's" teen allure. the number one seller on amazon is this, nearly 700 pages of economic theory by a frenchman. amazon cannot keep "capital" in stock. that's right, the most intense story line right now is not about zombies, it's the dramatic rising reality of income inequality, people want to know how the story will end. >> this shows that, you know, this issue about income and wealth are too important to be left to economists. i think it's for everyone. >> reporter: thomas picketty lays the issues out plainly. >> if everybody has share in the national wealth, that's fine. it's perfectly fine. if it gets concentrated in terms