S1·E21 Need to Know / Red Snow

On a little town people started going crazy. Edward Sayers is sent by the senator to investigate. He makes the usual tests but doesn't find anything. He traces it to one person with a very special secret... A KGB investigator is sent to Siberia to investigate the deaths of communist party officials. Later, he discovers that Stalin's exiles are alive and well. He also discovers dead people drained of blood.