I got up the blind of the nearer window as Bristol raised the other. Not a living thing was in sight from either!
Mostyn was beside me, his hand resting on my shoulder. I noted how he trembled. Bristol turned and looked back at us. The light from his pocket torch flashed upon the curator's face; and I have never seen such an expression of horrified amazement as that which it wore. Faintly, I could hear the constable racing up the steps from the hall.
Ideas of the supernatural came to us all, I know; when, with a scuffling sound not unlike that of a rat in a ceiling, something moved above us!
"Damn my thick head!" roared Bristol, furiously. "He's on the roof! It's flat as a floor and there's enough ivy alongside the water-spout on your house adjoining, Mr. Mostyn, to afford foothold to an invading army!"
He plunged off toward the open door, and I heard him racing down the Assyrian Room.
"He had a short rope ladder fixed from the gutter!" he cried back at us. "Graham! Graham!" (the constable on duty in the hall)—"Get the front door open! Get… " His voice died away as he leapt down the stairs.
From the direction of Orpington Square came a horrid, choking scream. It rose hideously; it fell, rose again — and died.
The thief escaped. We saw the traces upon the ivy where he had hastened down. Bristol ascended by the same route, and found where the ladder-hooks had twice been attached to the gutterway. Constable Graham, who was first actually to leave the building, declared that he heard the whirr of a re-started motor lower down Great Orchard Street.
Bristol's theory, later to be dreadfully substantiated, was that the thief had broken the glass and reached into the case with an arrangement similar to that employed for pruning trees, having a clutch at the end, worked with a cord.
"Hassan has been too clever for us!" said the inspector. "But — what in God's name did that awful screaming mean?"