Number One, the head of international terrorism organisation SPECTRE, plans to trap the British agent James Bond by using a beautiful Russian cryptographer and the promise of a Soviet Lektor decoding machine. SPECTRE Number Three Rosa Klebb, a Soviet double agent, grooms her British operative, Donald 'Red' Grant, for the mission, and selects the Russian Tatiana Romanova to lure Bond.

In London, Bond is summoned to see M, who tells him that Romanova plans to defect, that she has a Lektor device (which the British have been after for years), and that she is in love with Bond. They agree that it's an obvious trap, but the promise of a Lektor is irresistible.

Bond goes to Istanbul (observed by Red Grant and an unkempt-looking man), where he meets agent Kerim Bey. Bond checks into his designated hotel, and finds the room has been bugged. Grant leaves his car outside the Russian consulate, and drives off in another. When the Russians check the abandoned car, they find a dead Russian agent in it. Klebb tells Grant that the Russians will suspect the British.

Bey shows Bond a secret underwater canal that leads to a room beneath the Russian consulate from which they can spy on their activities. They recognise Romanova and a Bulgarian assassin named Krilencu.

Bey takes Bond to a gypsy settlement where he watches a fight between two women over the same man. This is interrupted by Krilencu's henchmen, who devastate the settlement. Grant is watching from a distance, picking off anyone who seems about to kill Bond. This helps Bond to an easy victory, and the gypsies hail him as a hero. The two gypsy women pay him a nocturnal visit.

The next day, Bond and Bey assassinate Krilencu. Bond returns to his hotel to find Romanova in bed. He is unaware that Klebb and Grant are filming them from behind a two-way mirror. Bond and Romanova are tailed by the unkempt man, who is killed by Grant. Bond finds the body, on which are plans for the Russian consulate. Bond and Bey study the plans, and Bey is suspicious about things seeming too straightforward.

Bond goes to the Russian consulate to make a visa application. At the same time, Bey sets off a tear gas bomb in the hidden room under the building. Bond escapes with Bey, Romanova Romanova and the Lektor.

They board the Orient Express. Bond and Romanova, posing as a married couple, get the same compartment. Bey recognises a Russian agent, Benz, on the train. He warns Bond, and the two of them confront and restrain Benz. On the way to the restaurant car, the train guard tells Bond that Bey and Benz have killed each other.

The train reaches Belgrade, where Bond sends a message to M to arrange for a British agent to catch the train in Zagreb. Grant kills the agent, Nash, and assumes his identity. He invites Bond and Romanova to dinner, but Bond is suspicious when he sees him ordering red wine with his fish.

His suspicions are confirmed when they return to their compartment and Bond finds that Grant has drugged Romanova. He tells Bond that SPECTRE has deliberately been keeping him alive so they can steal the Lektor for themselves. He and Klebb filmed Bond and Romanova making love, which they plan to plant as evidence, making their deaths appear as a romantic suicide pact. Bond asks Grant for a last cigarette, and Grant opens Bond's booby-trapped case. A fight breaks out, which culminates in Bond killing Grant.

Bond and Romanova flee the train, and overpower the pre-arranged SPECTRE agent, stealing his lorry. A helicopter gives chase, but Bond blows it up with his folding rifle. They reach a boat, but are assailed by SPECTRE men in powerboats. Bond disposes of them by setting light to leaking fuel.

Bond and Romanova arrive in Venice and check into a hotel. Klebb disguises herself as a maid and tries to steal the Lektor. In the ensuing fight, she threatens Bond with poison-tipped blades emerging from her shoes, before being shot by Romanova. On a gondola, Bond and Romanova throw the incriminating film into the canal.