It’s late September 2008. Storied Wall Street investment bank Lehman Brothers Holdings has gone bust, the U.S. government has bailed out the world’s largest insurance company, some of the country’s biggest banks are merging just to stay alive, and the world’s credit markets are frozen solid. Meanwhile, Congress is bitterly debating Treasury Secretary Henry Paulson’s $700 billion plan to buy toxic assets from ailing banks — a plan that will become the largest industry bailout in U.S. history.

These are unprecedented times. Democratic House Speaker Nancy Pelosi, 68, the first woman to serve in that position, is thrust into the spotlight...