Like a shrewd salesman who keeps his suitcase to the side, Thomas McCarthy's “The Visitor” doesn't immediately announce itself as a movie about immigration policy. Instead, this enormously affecting, thought-provoking drama does it the smart way – by seducing us with sympathetic characters and compelling scenarios, then holding all of it in escrow until we whip out the checkbook.

It's a vigorously heartfelt film about the necessity of culture, and the rare big-screen polemic that manages, quite elegantly, to close the deal. It's also one of those welcome projects that invites a talented character actor – in this case, Richard Jenkins, the pockmarked journeyman from “Flirting With Disaster” and “The Kingdom” – to shine in a lead role. As Walter Vale, a grief-worn widower who befriends and champions a pair of young Muslim aliens, Jenkins turns his trademark, drawn-down mien into an unforgettable profile of transformation.

To be sure, Walter – a tenured, middle-age economics professor – has become something of a higher-education zombie. He ignores his students. He skips meetings. He lazily recycles his syllabi. “I haven't done any actual work in a long time,” he shamefully confesses later, while in New York to present a paper that he co-wrote in name only.

Writer-director McCarthy – taking a firmer dramatic posture after the surreal, skipping lightness of his debut feature, “The Station Agent” (2003) – obliges the audience to imagine Walter as he was before his world deflated (in a sweet but fruitless attempt to connect with his dead wife, a concert pianist, he takes piano lessons himself).

And that's the difference between Walter and, say, Dennis Quaid's soul-sick, dead-wife-grieving professor in the recent comedy “Smart People.” A credibility of character.

Arriving in New York City, Walter is shocked to find jazz-fusion drummer Tarek (Haaz Sleiman, hugely endearing) and his bashful African girlfriend, Zainab (Danai Jekesai Gurira), living in his mothballed flat – but not half as shocked as the squatters themselves, who rented it from a scam artist in good faith. In a rogue gesture of kindness, Walter lets the desperate couple stay in the apartment.

Intrigued by Tarek's Afrobeat musicianship, he takes drum lessons from the affable Syrian, and begins to see the younger man as a surrogate son. “The Visitor” could have made a simple, swell little slice of life about music and friendship if McCarthy, in conspiring to have the undocumented Tarek arrested and held in immigration limbo by the government, hadn't aimed for something more invasive and, ultimately, satisfying. For while Tarek's deportation nightmare is sad, it chiefly serves to enhance Walter as somebody we understand.

The most painfully touching moment in the movie comes when Walter, who foots his friend's legal expenses and tries to console him from behind a cold, plastic partition, chases Tarek's headstrong mother (Hiam Abbass) down the stairs and begs her to stay in his apartment. He's not fighting against deportation, specifically; he's fighting for a lifeline of friendship, lest it slip out the door forever. Thus, McCarthy envisions immigration not as a question of politics, but a fact of interpersonal American necessity.

Sure, he cheats a bit. After all, few of us, immigrants or no, are as artistic, stylish and moderate as Tarek and Zainab. Undoubtedly, he shows us immigration at its best. But, as Americans, should we presume any less?

“The Visitor”
Stars: Richard Jenkins, Haaz Sleiman, Danai Jekesai Gurira
Behind the scenes: Written and directed by Thomas McCarthy
Rated: PG-13 for brief strong profanity
Running time: 1 hour, 48 minutes
Grade: A-