Welcome to Hollywood in the Seventies, a time when producers cared about movies, or, at least, gained credibility by saying so, and when good acting, or, at least the reputation of it, sold films.

Marathon Man is a picture of these times - a reputed director fresh from Midnight Cowboy, that film's star Dustin Hoffman, the magic of Laurence Olivier and Roy Scheider, still famous after Jaws. It broke New York's opening weekend record after The Godfather, which again tells you something about American movies in the Seventies.

Does it match such expectations? A few times, yes, closely, but for the rest it simply maintains momentum.

First the story. Thrillers have fast and intricate plots, but this one is more like a tangled ball of wool than a tapestry.

Babe (Hoffman) is a doctoral student at Columbia University, chasing his father's memory - he went there; something happened to him at the hands of Senator McCarthy; he killed himself - and Elsa (Marthe Keller). His brother, Doc (Scheider), is thought by Babe to be a businessman, but we know otherwise, as we've seen him in a series of spy-like scrapes in Paris. He's connected to veteran Nazi, Szell (Olivier), via Szell's sidekick Janeway (William Devane). Convinced that Doc has told something of value to Babe, Szell and his cohorts come after him. Babe triumphs, in a roundabout way, without resorting to gratuitous violence, but not before practically everyone is dead.

There's a decent plot in there somewhere, which doesn't make it onto the screen. There are too many loose ends. Prime examples include the father backstory, which ends as nothing more than cheap trauma for Babe. There's also Janeway, excellently played by Devane, who's wasted, muttering about The Division, for which he and Babe's father and brother worked. This is somehow tied to Szell, although you never quite find out how. There's also the case of Szell's brother, who dies in a car crash with an irate New York Jew at the start of the film, something Babe, on his morning run, stops to witness. That's good fun until you realise the impact of this seemingly inconsequential scene will never ripple through because there are too many additional strands in its way.

Also, there are a number of bizarrely botched scenes, which could have been avoided with a little more care and attention. It becomes clear at the beginning of the second act that some of the threads from the first count for nothing and the film is therefore scrambling to fill what the plot now requires to advance. And so the battle, inherent in the genre, between mood and slickness, credibility and stability, is lost.

John Schlesinger, nevertheless, is an invigorating stylist. The opening credits, in particular, are beautifully shot and cut and the first 20 minutes are the best from every point of view. After that, the realisation dawns that the director seems unable to adapt himself from Midnight Cowboy, as if New York is grafted onto the diamond district-Columbia hideaway worlds of these characters. However, there are lovely touches throughout and he's an expert at selling you the feint and almost as good at following up with a punch.

What saves the movie from being a good-looking mess is the acting. Olivier isn't given a lot of room by the writers, but plays well with what he has. One scene, long famous, involves a chair with straps, a dentist's drill and an alpha-plus performance from Sir Larry. It isn't the drill that makes your teeth ache so much as the quality of Olivier's craft.

Hoffman is full of energy, most of it pointing in the right direction, and Devane and Scheider are excellent. Only Marthe Keller, who learnt her lines for the screen test phonetically, because she knew no English, spoils things with her passivity.

If only Marathon Man had stuck to the course and paced itself through the race, it could have been a winner.