Over the decades, Roman Polanski has been attracted to characters in extreme situations; then he gets us into their heads. Think back to the deeply personal dilemmas of Rosemary Woodhouse in Rosemary’s Baby and Wladyslaw Szpilman in The Pianist. Polanksi is back in familiar territory with The Ghost Writer, and the film is an ever-growing exercise in tension and political intrigue.

The guy who’s never named  is a fast-working British ghostwriter who’s helped all sorts of over-the-hill celebrities get their memoirs into book form. When another ghostwriter who’s working on a book about a former British prime minister is found washed up on a Martha’s Vineyard beach, this new ghost (Ewan McGregor) is hired to take over the project.

Hewing very closely to the Robert Harris novel, the film immediately tosses our protagonist into this new world of working with a politician, then throws him up against a clock: He must take the pretty much useless work of his predecessor, interview his subject — one Adam Lang (Pierce Brosnan) — and crank out a completed book in one month.

But wait… McGregor’s character signs on the dotted line and is whisked from London to the Vineyard, where Lang is lounging around in a fantastic borrowed home with his sullen, angry, or maybe just lonely wife Ruth (Olivia Williams) and a battery of assistants and security folks. And then the hammer comes down. Lang is accused of committing war crimes during his former reign, the power people around him ask the ghost to help put out the political fires that spring up, and his publisher demands that he center the book on the supposed war crimes and — oh, yeah, finish it in two weeks, not a month.

Hell, there was enough going on here with the body washing ashore at the beginning to make for a good story. But Harris and Polanski turn it into a real corker of suspense.

A great deal of the film’s success has to do with Polanski’s elegant manner of framing shots and the placement of his actors. Most of the action is set amid cloudy, rainy, windy weather that’s perfect for the film’s dark mood. All of it is accompanied by Alexandre Desplat’s nervous, Bernard Herrmann-like score.

But it’s Ewan McGregor, as the ghost, who pulls it all together, who makes us worry about the ghost and wonder what he’s gotten himself into. We’re never told much about his character, but the ghost seems to approach his craft with nonchalance, maybe a little too much confidence that he knows what he’s doing and that everything will come together. Of course, it doesn’t, and McGregor soon puts on a look of worry that just keeps growing, as the people around him grow more and more enigmatic.

Among the enigmas is Lang, one of Brosnan’s most enjoyably despicable characters since Andy Osnard in The Tailor of Panama; the lovely Williams (Rushmore), who wears quite a few faces in this one; and as Lang’s right-hand woman Amelia, Kim Cattrall, who plays it note-perfect instead of displaying her usual habit of chewing the curtains.

The film does get a little too busy and convoluted when it briefly visits the mainland to add a couple more characters, but the murkiness that comes out of that eventually works smoothly into its framework. In the end, it leaves us to ponder what ghostwriting is all about. Yes, the object is to get to the bottom of things, but you’d better be careful not to ask too many of the wrong questions.