1967 was a fascinating year for thrillers. John Boorman sent Lee Marvin on a mythic quest for vengeance in Point Blank; Alain Delon was an ice-cool assassin in Melville's La Samourai; even the Bond saga reached dizzying heights of fantasy and excess in You Only Live Twice and its unofficial rival, the pop art Casino Royale. Meanwhile Bond producer Harry Saltzman released the third film in his Harry Palmer series, starring Michael Caine as the secret agent who is everything Bond is not — working class, bespectacled, cynically wary of the government agency that routinely stitches him up. Just as Point Blank and La Samourai, along with later films such as Altman's The Long Goodbye and the Coen brothers' The Big Lebowski, subvert the traditional codes of the crime thriller, so Billion Dollar Brain takes the sixties spy thriller and turns it inside out. It is closer to The Manchurian Candidate and Dr Strangelove than to The Spy Who Came in from the Cold or From Russia with Love.

Critics have generally been dismissive of Billion Dollar Brain. One reason for this lack of regard is that Billion Dollar Brain is the second sequel in an established series. The "law of diminishing returns" is held to apply — The Godfather Part II may be a masterpiece but number three stinks. Thus the first Harry Palmer film, The Ipcress File, is normally considered the best; the second, Funeral In Berlin, directed by Goldfinger's Guy Hamilton, is thought to be too complicated for its own good; and Billion Dollar Brain is dismissed as too fantastic.

The basic plot outline of Brain does indeed seem farfetched. Spy turned private eye Harry Palmer is instructed by a computerized phone message to take a package of eggs to Finland. It turns out that the eggs contain deadly viruses that Palmer's contacts, the American Leo Newbegin (Karl Malden) and his Finnish mistress Anya (Françoise Dorleac, in her final film) plan to smuggle into Soviet territory. Newbegin and Anya work for an organization called the Crusade for Freedom, controlled by the billion-dollar computer of the title and run from Texas by anti-Communist oil millionaire General Midwinter (Ed Begley). After a baffling series of crosses and double-crosses involving Palmer's former MI6 boss Colonel Ross (Guy Doleman) and his Russian counterpart Colonel Stok (Oskar Homolka), Midwinter's private army is eventually destroyed by Soviet missiles as it attempts a full-scale invasion of the Eastern bloc.

Brain's elements of fantasy, though, have a dark flavour far removed from the excesses of rival spy series such as those featuring Matt Helm or the Men from U.N.C.L.E. The opening shots of Palmer's seedy private detective office — all blinking neons and dark shadows — suggest the moral uncertainties of film noir; knocked unconscious at one point by a Russian soldier, Palmer awakes in a bath full of corpses; the Brain issues instructions to its agents in an unnerving mechanical drone anticipating HAL in 2001; the film climaxes with an army of white-clad storm troopers plunging to destruction through the Baltic ice. Scenes such as these have an overdone quality, but they effectively create a world where violence and hysteria are only just beneath the surface.

Even fans of director Ken Russell dismiss Billion Dollar Brain as an aberration, an early commercial diversion before he found his voice with ‘70s works such as The Devils, The Music Lovers, and Mahler. Yet a careful viewing of Billion Dollar Brain shows it consistent with Russell's personal vision, remarkably so for a mainstream thriller directed under contract. Most obviously there are the visual flourishes — a frozen corpse is discovered naked in a room lined with Victorian erotica, strange medieval murals decorate the Brain's Finland HQ, a brief sequence in a greenhouse is dominated by green overgrown plants that almost crowd out the actors. And then there is snow. Lots of snow. Russell uses the snow of his Finnish locations almost as imaginatively as David Lean used the desert sands in Lawrence of Arabia. Snow and sky highlight different moods — brilliant sunshine lends everything a harsh glare as Palmer makes his uncertain first contacts in Finland; thick snowdrifts under an ominous grey sky impede his progress on a dangerous sortie behind the iron curtain into Latvia; reflected sunlight turns to pitch darkness as the fascist convoys speed towards the sea, where the white floes will crack to reveal deadly black water. Throughout the film, characters are framed as lonely silhouettes against immense white vistas. Palmer and his associates struggle through the elements wrapped in heavy furs, their breath freezing in the air. We almost shiver with them. Russell gives us a film with ice in its soul.

Brain's striking visuals are complimented by John McGrath's script, which seems to deliberately subvert what we expect from an espionage film of the mid-1960s. First there is the character of Palmer himself. Whereas James Bond or Napoleon Solo confidently overcomes all obstacles to save the day, Palmer seems barely in control. Tricked, knocked out, set up by his own side, he drifts through the serpentine plot having little impact on the events around him. A Bond movie will usually climax with our hero desperately blowing up the villain's base seconds before civilization is going to be destroyed; the final defeat of Midwinter's force in Billion Dollar Brain is effected by the Russian Stok with no assistance from Palmer. Like John Lennon in Help! Palmer seems at times to be an extra in his own film. His only defense is a weary sarcasm, a verbal reflex that tries to puncture the increasing madness around him. In a world where demented generals plot war from computerized bunkers, perhaps the power of words is all we have. Palmer achieves one of his few real victories in the film when he hypnotically persuades General Midwinter to spare his life — James Bond would have just blasted his way to freedom.

If Palmer scarcely fulfills the role of hero, he has little backup from the traditional good guys of secret agent cinema. The relationship between Palmer and his MI6 controller Colonel Ross rarely rises above mutual contempt. "I'd be bloody grateful if you'd go," Palmer tells him during their first scene together. Palmer is the insolent foot soldier, forever needling Ross's upper-class officer. Harry Palmer also has no illusions about the patriotic nature of Ross's activities. "This is work of national importance," Ross tells him at the start of the film. Palmer's reply is derisively realistic — "What's the matter, Colonel, your mortality rate gone up?" Ross eventually coerces Palmer into cooperating by threatening to frame him for a murder in Finland. Once Palmer has reluctantly agreed and signed the Official Secrets Act, he is abruptly dismissed. "You don't mind walking back, do you Palmer? I've got a plane to catch," is all the thanks Ross gives him before driving off and leaving him stranded at a snowy roadside in the middle of nowhere. This is far from the deference and rapport that exist between M and James Bond.

Beside the reassuring support of the likes of Q and Miss Moneypenny, 007 can rely on the CIA's Felix Leiter to lend a hand. The American presence in Billion Dollar Brain is altogether more sinister. Karl Malden's Newbegin is a portrait of affable corruption. He betrays his wife through his affair with Anya, betrays his U.S. employers by creating a network of fictitious agents then pocketing their wages, and betrays his friend Palmer twice — setting him up to be killed in Latvia, then getting him arrested as a Russian spy in America — despite Palmer having saved his life during a previous assignment.

Newbegin is happy to let others die if it serves his own ends; his boss General Midwinter is even more dangerous. A close relative of Strangelove's Jack D. Ripper, he is a fanatical anti-Red who never leaves Texas — "I just don't like the air in other places." His feverish patriotic ranting, intercut with shots of chanting supporters dancing amid blazing crosses, deliberately evokes the Nazi rallies. Just as the 1960s saw another Texan, Lyndon Johnson, send U.S. forces into Vietnam, so Midwinter's insularity breeds an apocalyptic threat: his private army will trigger world war three by "liberating" Latvia. As he sonorously repeats, "My arm is long and my vengeance is total."

Billion Dollar Brain cleverly contrasts Ross and the Americans with the Russian Stok. Unlike Newbegin, he retains a trait of idealism. An old Bolshevik, he sadly quotes Lenin while sharing a drink with Palmer. Whereas the English and Americans see Palmer as a pawn to be used for their own ends, Stok seems genuinely concerned with his well-being, warning him about the true nature of the Crusade for Freedom. Stok's moral authority is emphasized when his men corner Dr. Eiwort (Vladek Sheybal), Newbegin's agent in Latvia. He grimly informs Palmer that Eiwort had been a Nazi collaborator, responsible for the deaths of women and children during the war. Here Billion Dollar Brain's flouting of traditional espionage thriller codes is at its most obvious: the KGB officer informs the English spy that his American allies are employing mass murderers. It is Stok's steely pragmatism — rather than Ross's cold patriotism or Midwinter's fervor — that ultimately resolves the film. As the Russian missiles destroy Midwinter's private army and avert world war three, we see the dawning of détente. Stok's final assessment of Midwinter shows his own acute understanding of cold war realpolitik: "He was a very stupid man. A patriot, of course, and very brave. During a war such men earn medals, win victories, we are proud of them. But at such a time as now — a little bit stupid."

Perhaps the dice are too heavily loaded in Stok's favour. The film mocks the counterrevolutionary Crusade for Freedom but makes only passing reference to the Soviet Union's crimes. A year after Billion Dollar Brain was released, Russian tanks crushed the Prague Spring, an act of ruthless efficiency the professional in Stok would have admired. The swift destruction of Midwinter's army can be seen as a grim forewarning.

Apart from two lackluster cable TV movies in the 1990s, Billion Dollar Brain was the last Harry Palmer film. Michael Caine quit the series after its release, claiming he had done all he could with the character. In a way he was right. Billion Dollar Brain stretches the espionage genre as far as it can go. It reaches beyond the confines of the spy thriller to show ordinary people caught up in the tide of history. They may be corrupt, idealistic, or just trying to survive as best they can — each is trapped by the politics of their time and place, powerless against the blind forces that send missiles crashing from the sky. With greater success than many more obviously political films, Billion Dollar Brain uses its pop thriller framework to reflect the frightening chaos as the 20th century hurtling towards the 21st. From the less than comforting prospect of 2003 we can look back and wonder how we made it this far.