Harry Palmer (Michael Caine), the reluctant secret agent from The Ipcress File (1965) and Funeral in Berlin (1966) -- both (like the source for this movie) based on novels by Len Deighton -- is back again in Ken Russell's Billion Dollar Brain. Having left Britain's espionage service, Palmer is scraping out a living as a private investigator, but he's still willing to give his old boss Colonel Ross (Guy Doleman) the bum's rush out of his office when he comes calling, offering a raise and promotion if he'll return. But Palmer ends up working for Her Majesty's government anyway -- a letter arrives, with a key and money, and telephoned instructions by a mechanical voice connect him up with a carefully sealed parcel (filled with what an x-ray reveals as eggs) that he must transport to Helsinki. No sooner does he get there than he discovers that an old friend, Leo Newbigin (Karl Malden), and his young lover Anya (Françoise Dorléac) are behind the trip, and that the man who was supposed to receive the parcel is dead. The eggs contain dangerous viruses stolen from a secret British laboratory, and England wants them back and wants to know why they were stolen. That assignment immerses Palmer in a deadly game of deception, double-dealing, and triple-crosses on all sides, as he finds that Leo is working for a privately operated intelligence network, set up by a rabidly right-wing Texas oil man, General Midwinter (Ed Begley Sr.).
The billion-dollar super-computer of the title, built by Midwinter, runs a network of spies and assassins aimed at the destruction of the Soviet Union. That interests Palmer's old friend, Soviet security chief Colonel Stok (Oskar Homolka, in an almost movie-stealing performance), very much, and he, too, wants to know what Palmer knows. And then there's Leo, who has taken millions from Midwinter, supposedly to establish a secret underground in Latvia, waiting for the signal to rise up against the Soviets occupying their country that will spread across the Baltics and beyond and bring down the Soviet government. He's taken the money, but all Harry find when he goes into Latvia is motley bunch of broken-down black marketeers whose orders are to kill him and make it look like the work of the Soviets. And there's Anya, who is sleeping with Leo, trying to seduce Harry, and seems to have an agenda all her own, but in whose interest? If it's all a little confusing, so was the book on which it was based, but there's enough striking visual material, courtesy of cinematographer Billy Williams, and engrossing performances (and a wry sensibility), courtesy of director Ken Russell and screenwriter John McGrath, that the leaps in plot, logic, and setting don't matter that much, and it is great fun.