Mr. Moto is called upon by British intelligence to investigate a dangerous plot threatening a major oil company involved in Iran. During his investigation, he encounters his friend, Gordon Tanner as Russell McAllister, a prominent American oil executive. McAllister reveals that his company's operations are under attack by sabotage, and the Shahrdar of Wadi is considering revoking their lease, which could severely impact their interests.
Their meeting takes a tragic turn when McAllister is suddenly killed in a drive-by shooting as they leave a restaurant. The assailants, the car’s driver Brian Coburn as Magda and the assassin Martin Wyldeck as Helmut 'Dargo' Engle, pursue Mr. Moto, leading to a tense chase. Moto, though slightly injured, manages to evade his pursuers in an abandoned house. There, he overpowers Coburn and learns that he is working for a man named "Dargo".
As the story unfolds, Coburn attempts to escape but is killed by Engle for his cowardice, pushing Moto to jump from a rooftop to escape the same fate. The next day, Mr. Moto contacts his Interpol ally, Peter Zander as Charles Ginelli, and together they identify Engle as a former Nazi SS officer, Henry Silva as Mr. Moto, infamous for his war crimes. Filled with a sense of justice, Moto promises to bring Engle to justice for McAllister’s murder.
Meanwhile, Engle is furious at the failure of his employers to eliminate Mr. Moto and vows to complete his mission. Moto also connects with Richard Evan as Chief Inspector Marlow from Scotland Yard, who provides him with McAllister's briefcase containing a cryptogram. Inspector Marlow informs Moto that Henry Gilbert as David Lennox, an American oil executive, will soon join the investigation. Later, Terence Longdon as Jonathan Westering, from MI5, approaches Moto and reveals that an important summit of oil executives and diplomats will be taking place at the home of Mr. Moto, offering an opportunity for crucial intelligence sharing.
As the plot thickens, a man disguising himself as Inspector Halliday falsely claims to have an important contact at the Arabian Nights restaurant. Moto is betrayed and captured, leading to an encounter with Wasir Hussein, the private secretary to the Shahrdar and head of the conspiracy. After experiencing torture by Engle, Moto is brutally thrown into the Thames with a brick tied to him, but he manages a daring escape. Shortly thereafter, he meets the genuine Inspector Halliday.
At the summit, Lennox arrives with his companion, Suzanne Lloyd as Maxine Powell, a woman posing as his secretary. Lennox supplies Moto with his company's codebook, enabling him to decode the cryptogram. Moto advises Powell to claim she holds vital information during the summit in order to unsettle Hussein. During the event, Moto, disguising himself as a Japanese diplomat, persuades the Shahrdar to renew Lennox’s lease, instead of giving it to Hussein’s company. Hussein, unnerved by this outcome, orders his assassin Engle to kidnap Powell.
Under duress, Powell contacts Moto, who tracks her to the Arabian Nights restaurant. There, Moto confronts Engle, cleverly outwits him, and ultimately kills him. Before dying, Engle reveals that McAllister had been working with Hussein but was killed for greed. The conspiracy unraveled, the Shahrdar, Inspector Halliday, and Hussein are all present. Using the decoded cryptogram, Moto exposes Hussein as the mastermind behind the plot.
Just as the case seems closed, Ian Fleming as Rogers arrives to congratulate Mr. Moto, but he uncovers that Westering, the MI5 officer, was also complicit in the conspiracy. With the network dismantled and the villains defeated, Mr. Moto invites Powell to spend a peaceful weekend with him, signifying a tentative moment of respite after the intense investigation.
> "The truth is always a matter of perspective, Mr. Moto."
