I?m very intrigued by this premise. Love the genre myself. But still a bit confused. Is he basically being made to do the right thing (catch a Nazi)? The dark past stuff is great for a broken type hero but shouldn?t he have a good guy goal?
Here?s a thought melding your two long lines (don?t know if it matches your script):
?A retired spy living the highlife on the French Riveria, must return to his old dangerous games to catch a Nazi war criminal. ?(23 words)
And you can still add a couple words about what pulls him back in (inciting incident), by starting logline with ?After blah blah blah, a retired spy ....?