His father addressed the select group around him: “Good friends. We have a little tableau to show you, from the seventeenth century—truly a miracle. How did they do it? My son will now present, ‘Non angli, sed angeli.’”

A handful of tourists paused as Max took the stage. “In just a few minutes, a beam from the sun will shine through a tiny hole in the window up there”—he raised his finger—“and hit the floor at this place, as it has every Midsummer’s Day.” He gestured at the metal talon, and continued: “You can see this concave mirror has been placed so it can direct the light through the crystal we have clamped, there.” He squatted to demonstrate the objects with all the esprit of an apprentice television presenter, and Grace and Lucy exchanged amused glances. Max warmed to his task.

“Dr. Dee’s small crystal will divide the beam,” he said, pointing at it, “then one section of it will bounce off this mirror and light up the white card—which is here. The other part of the light will bounce from the other mirror, there, onto this plate, which may have been hand-crafted hundreds of years ago by the artist Dürer. It’s called ‘three.’ We need a bit of luck”—Max laughed—“but if we’ve got the measurements right, it should hopefully create an image of the angel, which will float in midair in front of the card.”

Lucy was getting tangled, and laughed aloud—Max’s grasp of science almost eclipsing her own. She wondered if a preoccupied Alex had slightly denied the little boy some of his childhood, and made a note to herself to bake with him and ride bikes as often as possible.

“The equipment you can see here has just been found among a collection of things from the sixteenth or seventeenth century. Today a laser beam would be better than the sunlight, and the image would be a photographic hologram. But we want to see if we can get any kind of result from the sunbeam. Watch! It should happen any second.”