He listened quietly, staring off into space, and I assumed he was collecting his thoughts for an answer, but a few minutes later he cleared his throat and shook his head. That, he explained apologetically,
was outside his area of
specialization. His interest was in interest rates, and he hadn't given military
economics much thought. He suggested I see Dr Wessey, who once did a paper on War Trade
Agreements during World War II. He might be able to help me. Before I could say anything else, he
grabbed my hand and shook it. He had been glad to meet me, but there were some notes he had to
assemble for a lecture. And then he was gone.

Revise the first sentence into a sentence that "tells" instead of "shows."