Mrs. Which tells them that Mr. Murry is behind the shadow, and that that's where they must go to find him. Mrs. Whatsit explains how they travel through time and space so quickly: it's a tesseract, a wrinkle in time, that takes them through the fifth dimension. The group tessers again, stopping briefly on a two-dimensional planet that doesn't work very well for the human members of the party, and arrives on a grey, foggy planet that is the home of the Happy Medium