With one exception, the characters’ teeth in the movie have been filed. Unlike those in the book, who speak through e-mails, diaries, letters and interviews, the characters here leave the impression of giving harmless nibbles instead of flesh wounds. Defanged and pushed into the background, the satire vanishes, and you are left with an agreeable romantic comedy in which a progressive Islamic sheik gently promotes international cooperation and togetherness.

The bracingly nasty dental exception is Kristin Scott Thomas’s portrayal of Patricia Maxwell, the press secretary for the British prime minister. She doesn’t speak her dialogue so much as snap it in a tone of icy disdain so acute that you half expect to see blood foaming from her mouth after each remark. If her performance adds a discordant note to the sweetened film, it is a necessary one. Without her presence the movie might have collapsed into a mushy soufflé.

The silliness begins as a scheme is floated by a visionary sheik (Amr Waked) with unlimited financial resources to turn a Middle Eastern desert into a recreational paradise for sport fishermen. It is also an exercise in international relations. Played by Mr. Waked as a starry-eyed New Age mystic who somewhat resembles the young Ben Kingsley in his quasi-religious mode, he is given to spouting inspirational mumbo-jumbo.

“For a fisherman, the only virtues are patience, tolerance and humility,” he intones with a priestly gravity.

An avid fly fisherman who has a Scottish estate, the sheik envisions a Herculean water management project that involves the creation of a salmon run in which the fish can swim upstream to spawn. Not only will it bring his favorite leisure activity closer to home, he declares, but it will also help his people.

When the plan is proposed to the British government by the sheik’s assistant, Harriet (Emily Blunt), Patricia seizes on it as an opportunity to distract the public from Middle Eastern conflicts and score political points for her boss.

Dr. Alfred Jones (Ewan McGregor), a British fisheries expert who goes by Fred, is approached to evaluate the feasibility of the concept, which would involve importing 10,000 North Atlantic salmon to Yemen from Britain. Believing the plan to be preposterous and impossible to carry out, he dismisses the idea. But Patricia, whose research reveals that two million British voters are fishing buffs, will not let it rest. She pressures Fred’s boss to force his participation.

An unexpected uproar ensues when British fishermen learn that their salmon stock will be depleted. It is decided that the only solution is to use farmed salmon, which have no river experience. Thus the big question: Will farmed salmon follow their wild cousins’ instincts and leap upstream?

Mr. McGregor has a delicious role in Fred, a buttoned-up, unhappily married bureaucrat whose cold, nasty wife of two decades leaves him for months at a time to conduct business in other places. He develops an unspoken romantic attraction to Harriet, whose boyfriend, Robert (Tom Mison), is fighting overseas. When she receives the news that Robert is missing in action, she falls apart.

Whether Harriet and Fred will get together is a question that hovers over the movie. The appeal of the film depends on the charm of Mr. McGregor and Ms. Blunt, whose polite but discreetly charged connection is the story’s emotional center.

The uptight Fred is a nifty departure from Mr. McGregor’s typically roguish roles, and he sufficiently camouflages his romantic magnetism to reduce the gleam to a distant twinkle. Ms. Blunt’s Harriet is demure and ravishing.

The movie is burdened with a perfunctory subplot in which the sheik becomes the target of an assassination plot by Islamic extremists. The biggest moment of suspense has nothing to do with international politics or terrorism. It comes when those farmed salmon are finally released into the waters of their new home. Will they mill around in confusion or will they jump? It is enough to say that for this moment to be the film’s dramatic turning point is an indication of its softness.