Spotlight, film review: Michael Keaton shines in this chronicle of atrocities

"Forget it, Jake, it's Chinatown," is the famous line at the end of Roman Polanski's thriller, Chinatown. Its implication is clear – the corruption that private eye Jake Gittes encounters in 1930s LA is so deeply engrained that it can't be cleaned out. A similar fatalism is evident at some moments in Thomas McCarthy's Spotlight. This is a film based on a true story. The setting is Boston in 2001. The corruption in question here is the persistent abuse of children by the city's priests. It has been going on for years and is akin to a "cottage industry", and yet no one has been prepared to confront it.

Spotlight is an old-fashioned film that tells its story in a painstaking and thoroughly absorbing fashion. It's the kind of movie that you could imagine Henry Fonda or James Stewart starring in as decent, upstanding journalist heroes who refuse to give up on their story in the face of considerable difficulty and intimidation.

What is most impressive in writer-director McCarthy's approach is the lack of flashiness. Everything here, from the camerawork to the performances, is deliberately low-key. Much of the action unfolds in offices and archives. Spotlight has been compared to Alan J Pakula's Watergate film All the President's Men but there is no "Deep Throat" here. The journalists don't meet their sources in underground car parks. They're just doing their jobs, but in a remarkably diligent and conscientious fashion.

The film takes its tone from one of its central characters, the new editor of The Boston Globe, Marty Baron (Liev Schreiber). He's from out of town. He is Jewish, not Catholic. Baron is an aloof figure, not the type to joke or drink beer with his staff at baseball games, or be taken in by the false bonhomie of the local cardinal. He notices a short news item about an abusive priest and suggests to his sceptical staff that this could be a good local story to follow up on.

One of the ironies is that the Globe isn't exactly telling its readers anything they don't know. The newspaper has already reported on the subject, and there have been various claims from victims against the priests who abused them when they were children. These claims, though, have been settled for derisory sums. Any potential scandal has been hushed up.

McCarthy and his co-writer, Josh Singer, are very good at showing how the city's institutions are all interlinked. The senior Catholic clergy know the civic authorities, who know the politicians, who know the university rectors, who know the newspaper publishers, who know the business leaders. It's a tight-knit world. Many of the city's most influential figures were at the same Catholic schools or colleges – and that is one reason why the scandal of the abusive priests is being ignored. "If it takes a village to raise a child, it takes a village to abuse them," is how one character sums up the complicity.

Action scenes are in short supply. The only real motion comes from Mark Ruffalo's Mike Rezendes, a hyperactive journalist who is always in a hurry, always agitated. He is one of the Spotlight "special investigations" team. They enjoy time and resources that, in a new digital era, few newspapers grant to reporters. They're also, on the evidence here, so dedicated to their jobs that they have no time for private lives. McCarthy shows the reporters off-duty in passing. Ruffalo's character is separated and living on his own in a tiny apartment. The others are fleetingly seen in their kitchens or at dinner with spouses, but the film has nothing resembling a romantic subplot.

After his flamboyant turn as a movie star on Broadway in Birdman, Michael Keaton is in a more restrained groove as Walter "Robby" Robinson, the leader of the Spotlight team. He's the brow-furrowed, pencil-chewing exec, ferreting away at a story that involves the misdeeds of people and institutions he has dealt with all his life. He looks dapper in a middle-management way, equipped with crisp new shirts for every scene. It's a fine character performance, a world away from Beetlejuice. This is an ensemble piece in which all the Spotlight journalists are given their moments. Sacha Pfeiffer (Rachel McAdams) conducts the most probing interviews with victims. Matt Carroll (Brian d'Arcy James) is a seemingly mild-mannered reporter, indignant that paedophile priests live in his own community. There are strong supporting turns, too, from Stanley Tucci and Billy Crudup as lawyers on different sides of the fence.

Occasionally, the film begins to sermonise, to become earnest and a little self-congratulatory. Its view of journalism is closer to George Clooney's Ed Murrow movie, Good Night, and Good Luck , than the more sordid vision offered in Hack Attack, the book about British tabloid excesses that Clooney is trying to adapt for the screen. There are missed opportunities here. In one of the most poignant scenes, Pfeiffer doorsteps a priest who shares jaw-dropping insights about both his own predatory behaviour and what was done to him when he was a child. Yet the door is quickly shut on cycles of abuses that stretch back a generation.

Spotlight stands as a companion piece to Alex Gibney's 2012 documentary Mea Maxima Culpa: Silence in the House of God, also about clerical abuse of minors. Both start as local stories but as the evidence builds, so does the extent of the abuse they are chronicling. In Spotlight, what seems like a Boston story turns out to have a depressing universality about it. The Globe is not going after a few rogue priests. It's the entire system that is rotten.

There is a line late in the film that hints at the challenge faced by both the journalists and the film-makers. "No one wants to read about kids being raped by priests," it is observed. McCarthy is dealing with grim subject matter but the film has the momentum of a well-told detective thriller. His trick is to pay such close attention to the mechanics of the investigation that even the smallest breakthrough (a name spotted in a records book, a link identified in a microfiche cutting) seems intensely exciting.