Tom studied the moonbeam, with an idea growing in his mind. From the direction in which the beam came, he saw that the moon must be shining at the back of the house. Very well, then, if he opened the door at the far end of the hall—at the back of the house, that is—he would let that moonlight in. With luck there might be enough light for him to read the clock-face.

He moved down the hall to the door at its far end. It was a door he had never seen opened—the Kitsons used the door at the front. They said that the door at the back was only a less convenient way to the street, through a back-yard—a strip of paving where dustbins were kept and where the tenants of the ground-floor back flat garaged their car under a tarpaulin.