Under the call sign “Mark,” a Soviet illegal intelligence officer operates on U.S. territory. Over the years, he managed to build a powerful agent network and send many valuable pieces of information to Moscow. To make “Mark’s” work easier, a radio operator named “Vik” was sent to help him. But the newcomer couldn’t withstand the tension of a clandestine life and soon betrayed “Mark” to American special services—then surrendered himself. Urgently, the KGB leadership develops a plan to save their intelligence officer. And to search for “Vik,” a special group “Don” led by Major Pavel Semyonov is dispatched. For the fearless fighters, punishing the traitor becomes a matter of honor…