Passport To Peril - Robert B.  Parker John Stoddard is traveling from Vienna to Budapest just after WW II to see if he can locate his brother, a navigator in a plane that was forced down after it ran out of fuel, calculations for which John had been responsible. Unable to obtain a visa from the Russians, John pays for a forged passport and visa only to discover on the train that a young woman thinks he is someone else and he has the passport of a man wanted by several governments because of some information he has and who was killed just before John left the country. Soon the Russians, OSS, and ex-Nazis are chasing John around trying to discover what names were in the envelope that the murdered man had given to the girl.

This is by Robert Bogardus Parker who died in 1955, long before Robert Brown Parker wrote his Spenser novels, and it's based in part on his personal experiences in eastern Europe (although the use of the formal Sie instead of Du when the German boss is talking to his underlings was a little jarring.

Amusing story but nothing great. Interesting that it was republished by Hard Case because it doesn't really fit with their normal run of titles.