It's the late 19th century, and British astronomer Sanford Thayer has won international funding for his scheme to excavate an equilateral triangle, 300 miles to a side, from the remote wastes of Egypt's Western Desert. The 900,000 Arab fellahin have been put to work on the project, even though they can't understand Thayer's obsessive purpose. They don't believe him when he says his perfect triangle will be visible to the highly evolved beings who inhabit the planet Mars, signaling the existence of civilization on Earth.