Assignment: Vienna

Before Jake can turn over to Major Caldwell microfilm identifying 12 gangland leaders at a summit conference, they're attacked by a group of thugs. After Caldwell is wounded in the scrimmage, Jake must leave him behind at the hospital and takes Susan with him to get the microfilm delivered.

Jake is hired by Aline Masterson of a New York museum to recover the Royal Crown of Bosnia, stolen from her outside the Hofburg Museum. Through underworld contacts Jake delivers the pay-off money to a hijacker. When Jake is knocked unconscious at the rendezvous site, both he and Aline are suspected of being confederates.

Annalisa, a former girlfriend, reenters Jake Webster's life by asking him to prove the innocence of her husband, jailed by the Vienna police for the murder of his associate in valuable oil leases. Jake's curiosity is aroused when Karafatma, a wealthy Turk, warns him not to investigate.

Major Caldwell believes Jake Webster was the real target when an elderly flower lady is killed outside of Jake's Bar. However, Jake suspects another motive. He decides to investigate one of the three mourners at the old woman's funeral.

Jake uses a painting to find a royal emerald stolen by a convict, the painter of the portrait, in 1886. The painting leads him to a tunnel under the Hofburg Palace filled with plaster models of monuments. Jake must contend with several other crooks who are also after the emerald.

Jake Webster is startled to meet in Vienna Charley Stokes, whom he saw killed on a beach in Albania after the pair had blown up a power installation. Charley explains that, though seriously wounded, he was saved by Elga Compani, number two official in the Albanian Secret Police and is now married to Charley. Jake begins to suspect that Charley and Elga are still loyal communists.