Marlowe was waiting.

“Come right in,” he said. “Have a drink. You take it strong in Norway, don’t you?”

Knut smiled.

“Not so strong as you take it, Dr Marlowe.”

Marlowe motioned Jensen to an easy chair by the log fire (so beloved by many who live in centrally heated houses), and after moving a large cat from a second chair, sat down himself.

“Lucky you rang, Knut. My wife’s out for the evening, and I was wondering what to do with myself.”

Then, typically, he plunged straight to the issue — diplomacy and political finesse were unknown to him.

“Well, what’ve you got there?’ he said, nodding at the yellow box that Jensen had brought.

Somewhat sheepishly, Knut took out the first of his two pictures, one taken on 9 December 1963, and handed it over without comment. He was soon gratified by the reaction.

“My God!’ exclaimed Marlowe. “Taken with the 18-inch, I expect. Yes, I see you’ve got it marked on the side of the plate.”

“Is there anything wrong, do you think?”

“Nothing so far as I can see.” Marlowe took a magnifying glass out of his pocket and scanned carefully over the plate.

“Looks perfectly all right. No plate defects.”

“Tell me why you’re so surprised, Dr Marlowe.”

“Well, isn’t this what you wanted me to look at?’

“Not by itself. It’s the comparison with a second plate that I took a month later that looks so odd.”

“But this first one is singular enough,” said Marlowe. “You’ve had it lying in your drawer for a month! Pity you didn’t show it to me right away. But of course, you weren’t to know.”