The year is 1942, and Europe is at war. Captain Victor Nikiforov, an intelligence operative for the NKVD, has been trapped in Berlin by the German invasion of the USSR. Posing as a Nazi industrialist, his days are spent charming information out of Axis diplomats to try and keep the Red Army fighting another day.
Yuuri Katsuki, a foreign-educated bureaucrat in the Japanese Embassy, has secrets of his own concealed beneath his unremarkable demeanour. When he uncovers Victor’s real identity, it will alter the course of both of their lives forever.
Honestly one of the best period/historical gay romances I've ever read. Technically it is fan fiction, featuring characters from Yuri!!! on Ice anime series, but you don't need to have seen the show to enjoy this story.