SPECTRE's expert planner Kronsteen devises a plot to steal a Lektor cryptographic device from the Soviets and sell it back to them while exacting revenge on Bond for killing their agent Dr. No. The Spectre Number 1 puts ex-SMERSH operative and Number 3 Rosa Klebb in charge of the mission. Klebb recruits Donald "Red" Grant as an assassin, and Tatiana Romanova, a cipher clerk at the Soviet consulate in Istanbul, as an unwitting pawn, as Romanova thinks Klebb is still working for SMERSH.
In London, M tells Bond that Romanova has contacted their "Station 'T'" in Turkey, offering to defect with a Lektor, which MI6 and the CIA have been after for years; however, Romanova has stated she will only defect to Bond, whose photo she has allegedly found in a Soviet intelligence file. Bond then flies to Istanbul, where he meets station head Ali Kerim Bey. Bond is followed from the airport by the Russians and by Red Grant. Grant kills the Russian driver and Kerim Bey's office is bombed with a limpet mine in retaliation. The next day, Bond and Kerim Bey spy on the Soviet consulate, where Kerim Bey sees rival agent Krilencu. At night, Kerim Bey and Bond go to a rural gypsy settlement, which suffers an attack by Krilencu's men, who wound Kerim Bey and nearly kill Bond, who is saved by a hidden Red Grant. On the following night, Kerim Bey kills Krilencu with Bond's sniper rifle. When Bond returns to his hotel suite, he finds Romanova in bed waiting for him, with both of them unaware that they are being filmed by SPECTRE.
The next day, Romanova heads off for a pre-arranged rendezvous at Hagia Sophia. The bespectacled man who followed Bond to the airport tries to intercept Romanova's floor plan of the Soviet consulate, but is killed by Grant. Upon finding the body, Bond takes the floor plan, and brings it to Kerim Bey to plan their theft. After stealing the Lektor, Bond, Romanova, and Kerim Bey escape with the device on the Orient Express. On the train, Kerim Bey and a Soviet security officer named Benz are killed by Grant, who makes it appear as if they killed each other. At Zagreb, Grant leaves the train, kills agent Nash from Station Y and boards it again to meet Bond, pretending to be Nash. He drugs Romanova at dinner, then overcomes Bond. Grant taunts him, boasting that SPECTRE has been pitting the Soviets and the British against each other, and claims that Romanova thinks that "she's doing it all for mother Russia". Grant also mentions the film of Bond and Romanova at the hotel suite, saying that after both are killed, Grant will plant it in her handbag along with a forged blackmail letter so it looks like it was a murder-suicide. Bond tricks Grant into opening Bond's attaché case in the manner that detonates its tear gas booby trap in his face, allowing Bond to attack him. In the ensuing struggle, Bond eventually manages to stab Grant with the knife hidden in the attaché case and strangles Grant to death with his own garrotte. At dawn, Bond and Romanova leave the train, hijack Grant's getaway truck, destroy an enemy helicopter, and drive to a dock, eventually boarding a powerboat.
Number 1 is displeased, and summons Kronsteen and Klebb. He reminds them that SPECTRE does not tolerate failure, and brings in agent Morzeny to then execute Kronsteen with a poisoned spike in the toe of his shoe. Number 1 tells a frightened Klebb that she now has total control of the mission and has one last chance. Klebb sends Morzeny after Bond with a squadron of SPECTRE's boats. Morzeny nearly catches Bond, but the agent sets his pursuers' boats on fire with a signal flare. Bond and Romanova reach Venice and check into a hotel. Klebb, disguised as a maid, attempts to steal the Lektor. She attempts to kill Bond with both a gun and her poisoned toe-spike, but ends up being shot by Romanova. Riding in a gondola, Bond throws the film of him and Romanova into the water as they are rowed away.