Sickan, the leader of the criminal Jönsson gang is incarcerated in a mental institution, attended by Dr M.A. Busé, who admire a handbook in crime that Sickan has been writing. Blackmailed by the nefarious banker Wall-Enberg, Dr Busé and Sickan's partners Vanheden and Dynamite-Harry execute Sickan's plan of stealing the valuable Black Diamond of the Romanovs from the National Museum.
When Vanheden and Dynamit-Harry tries to break doctor Busé out of jail, they get Herman Melvin instead. He has been working at the Swedish Mint and the doctor, who has started to think like Sickan, has written a plan for making a burglary there, on Melvin's back. However, something goes wrong. They don't get a lot of Deutsch-marks as they planned but instead, they end up on a ship going to Poland, together with bunches and bunches of Polish Zlotys (the Polish currency). In Poland, they discover that the mafia are very interested in that money and Wall-Enberg is working with the mafia.
Harry Lund is having a bad day. First he gets fired. And then loses his entire fortune at an illegal gambling club. On his way out, he is assaulted and drugged by unknown men, and wakes up in a car with another man. A very dead man. A very murdered man. And Harry's penknife sticks out of his body. Harry flees in panic to Stockholm. And now not only the bad guys are close on his heels - but also the police...
Someone is killing off Swedish military officers and making it look like the works of Soviet agents. Hamilton has to crack the case before all hell breaks loose and there is a full scale spy-war with the soviets.
