Assignment: School for Spies — Edward S. Aarons

They yelled “treason” and then they fired him.

After years of death-dealing, near-suicidal service, Sam Durell was tossed out on his ear by the CIA. Get out of Europe, they told him, get out and don't ever come back.

Durell refused.

But nobody says “no” to the CIA, and so they went after Durell the way they'd hunt down any common traitor, any enemy spy -- with guns in their hands and orders to kill on sight…