Daniel found these moments slightly unnerving. For the most part she did not look like Isaac—not even the young, frail, girlish Isaac Daniel had met at Trinity half a century ago. He would never have guessed she had a drop of Newton-blood in her veins if he hadn’t known as much already. But during the moments when she forgot to hide her cleverness, a family resemblance flashed forth, and he saw Isaac’s face for an instant, as if the author of Principia Mathematica were stalking him through a darkened room when lightning struck outside.