SOLVED. Photographic memory, Europe, Circus, Mystery, 1970s or 80s

[Angie]

Back in the mid 80's I read a paperback mystery about a man who was a secret agent type guy. He had a photographic memory. At some point there was a circus and a woman and a train chase. He was carrying or trying to recover some soviet secrets on microfilm or something and when he got it he wouldn't look at it for ethical reasons because of his photographic memory. I'd love to know the name of the book to re-read it. I think the pb cover was orange.

[Angie]

The mystery was in that vein of Ross MacDonald type vintage crime/mystery ...

[Ann aka Iftcan]

Circus possibly? I believe that was about when I read this book. But I don't remember if he has total recall or not. But from the rest of the description, this was what I thought of.