David smiled in a superior way.

"That's just where--you're wrong--Knott--we relieve the--younger
men--that's our job--and I'm proud to--"

Peter Knott's kindly old eyes twinkled at the thought of David tackling a
lusty cracksman, twinkled and then became grave.

"Supposing you get laid up, injured in some way?" he asked.

"We don't think about that." David's expression was serene. "I go
on--duty at--two--very quiet then--lovely it is--on fine nights--when
I've been working--to get out--into the cool air--"

As David spoke Peter Knott pulled out his watch again and then got up.

"I saw your cousin Herbert a few days ago, Saunderson. He said he hadn't
seen you for a long time, wondered whether you'd go down to Rendlesham
for a few weeks. He wants a catalogue of his prints, and there are some
old manuscripts he would like your opinion about. I'm going down this
week-end. What shall I tell him?"

David put down his pipe.

"Tell him--I'm much obliged--later on perhaps--I can't--leave my
duties--while these Zeppelin scares last. They need experienced
men--one doesn't know what--may happen." He had got on his feet and had
gradually reached the door of the tiny flat. "Good-bye, Knott," he said
as he took the other's hand. "Don't forget--about Macmanus
and--Plimsoll--"