Reposted from Chat...
Help! This has been driving me slightly bonkers. I can't remember the name of the book or the author (I thought it was Frederick Forsyth, but it doesn't seem to be). All I really remember is that the hero is captured near the end in Russia, and scheduled to be executed, but somehow an old friend who owes him a favour swaps places with him, and is executed in his place. I have a vague feeling that they may be American, and possibly the favour is because of something that happened in the Vietnam War. Maybe. It's also entirely possible that they are British and I'm thinking of something else there...
Any ideas..this is really driving me crazy!!