Dr. Bird's voice was cut short by the sound of a pistol shot from the roof, followed by two others. The Irishwoman dropped Bolton and slumped into a sitting position and screamed lustily. Bolton and Dr. Bird, with the two operatives at their heels, raced for the roof. Before they reached it another volley of shots rang out, these sounding from the rear of the building. They made their way to the upper floor and found a ladder running to a skylight in the roof. At the foot of the ladder stood one of Carnes' party.
"What is it, Williams?" demanded Bolton.
"I don't know, Chief. Carnes and the other two went up there, and then I heard shooting. My orders were to let no one come down the ladder."
As he spoke, Carnes' head appeared at the skylight.
"It's the right place, all right, Doctor," he called. "Come on up, the shooting is all over."
Dr. Bird mounted the ladder and stepped out on the roof. Set on one edge was a large piece of apparatus, toward which the scientist eagerly hastened. He bent over it for a few moments and then straightened up.
"Where is the operator?" he asked.
Carnes silently led the way to the edge of the roof and pointed down. Dr. Bird leaned over. At the foot of the fire escape he saw a crumpled dark heap, with a secret service operative bending over it.
"Is he dead, Olmstead?" called Carnes.