Police in Argentina have foiled a plot to smuggle cocaine to Europe through the Russian embassy's diplomatic courier service, following an elaborate sting operation involving a shadowy Moscow intelligence chief.
Five suspected members of the drug gang, including a former accountant at the embassy and a Buenos Aires police officer, have been arrested in Argentina and Russia.
But the alleged head of the network, a mysterious Russian businessman known only as "Señor K", remains at large.
The plot was discovered by the Russian ambassador in December 2016 when he came across nearly 400kg of the drug inside 12 suitcases in an storage facility belonging to the diplomatic mission.
The ambassador, Viktor Koronelli, immediately informed the Argentine authorities, who seized the cocaine.
The haul was of "maximum purity" and worth €50 million ($84m) on the Russian market, Patricia Bullrich, the Argentine security minister, said as she revealed the operation on Thursday.
The discovery of the drugs was kept secret while Russian and Argentine security services collaborated on the year-long sting.
It finally culminated in a clandestine mission by the secretary of Russia's Security Council, Nikolai Patrushev, a career spy who as former head of the FSB is believed by British authorities to have probably approved the 2006 London assassination of Alexander Litvinenko.
Argentine police replaced the cocaine with flour and implanted tracking devices in the cases, before embarking on a lengthy monitoring operation and investigation in conjunction with Russian authorities.
The gang then left the dummy narcotics in the warehouse for almost a year, as the retirement of the conspiring embassy accountant had caused them to look for other routes. But after alternative options fell flat, the network returned to its original plan.
The former accountant, Ali Abyanov, was instructed to request his belongings be returned to Russia using the courier service, and, learning of the move, investigators prepared to pounce.
It was then, in December 2017, that Patrushev paid a visit to Argentina. Publicly, the purpose of the security tsar's trip was a meeting with Mauricio Macri, the Argentine president, in the Casa Rosada, where the pair signed memorandums of understanding.
But secretly, Patrushev - who rose through the KGB before becoming the head of its successor agency the FSB - had another mission.
Russian security services arranged for the delivery requested by Abyanov to be carried by Patrushev's plane, and the intelligence chief duly escorted the suitcases full of flour to Moscow on December 9.
Four days later, two gang members, Vladimir Kalmykov and Ishtimir Khudzamov, were arrested when they tried to retrieve the suitcases, while Abyanov was arrested simultaneously.
The main phase of the operation finally ended on Wednesday with two arrests in Argentina: of Ivan Blizniouk, the Buenos Aires police officer who allegedly purchased the cocaine and arranged for it to be stored at the embassy; and of Alexander Chikalo, a local mechanic of Russian nationality accused of having transported the suitcases to the airport.
Interpol are now hunting for the alleged leader, "Señor K", a well-connected businessman wanted by Moscow and believed to have been living in Germany in recent years.
The millionaire arranged the drug runs under the guise of a front company trading in exclusive alcoholic beverages, and according to files seen by Clarin, the Argentine daily, is believed to have previously carried out two successful shipments to Russia through Uruguay.