Prolific writers tend to repeat themselves, and so do prolific filmmakers. That’s certainly the case with Woody Allen, who’s pretty much turned out a movie each year for decades. At first they were comedies, and it wasn’t long before people began noticing similarities among many of them. Then Allen grew more serious—or at least serious more often—and his dramas began to share themes too. Certainly that’s the case with the London-set “Cassandra’s Dream,” which treats of the same issue of crime, guilt and punishment (or lack thereof) that marked 1989’s “Crimes and Misdemeanors” and his first English-made film, “Match Point” (2005). It’s not a bad film, but it does seem rather an unnecessary one, since it’s very weak compared to the first and no improvement on the second.

The tormented souls at the center of the plot are two Cockney brothers, Ian and Terry Blaine (Ewan McGregor and Colin Farrell). Ian is a slick striver whose desire to find some get-rich investment scheme (the latest, a California hotel project) is stymied by the need to help his dad (John Benfield) at the family restaurant. Terry, by contrast, is an inveterate gambler and drinker who works as a mechanic in someone else’s garage. But despite their problems, they decide to go in together on a used yacht that they christen Cassandra’s Dream, after a dog Terry’s bet on very profitably.

The boys might have known better than to give their purchase that name had they been better educated. Cassandra, of course, was a figure of Greek myth whose prophecies were cursed to be ignored—and foretold disaster anyway. She’s a harbinger of bad things to follow, as Allen, who’s made classical references before (remember “Mighty Aphrodite,” with its Greek chorus) surely wants us to understand (and by tossing in a later allusion to Greek tragedy he adds the warning that Ian and Terry are headed for an unhappy end). As if all that weren’t enough, in response to Ian’s remark after the yacht purchase that his California deal means his ship will come in, his dad (who otherwise appears a fairly uneducated fellow), again refers to Greek myth when he replies that the only ship you can be sure will come in is the one with a black sail. That points back to the story of Theseus and the minotaur: as a boy going to Crete to face the beast, he told his father, the Athenian king Ageus, that if he was coming back alive, he’d change the black sail he left with for a white one (of course, he forgot, leading his father, at sight of the ship, to commit suicide by leaping into the sea, which was henceforth called the Aegean).

So tragedy is on the menu, and Allen doesn’t disappoint. Ian falls for Angela (Hayley Atwell), an actress, by passing himself off as a successful entrepreneur, and so desperately needs the cash for his hotel investment. Terry is even more needy; he loses big on cards and finds himself threatened by some not-very-nice collectors. The apparent answer to both their problems is their Uncle Howard (Tom Wilkinson), a wealthy plastic surgeon, who offers them the money they require but asks a favor in return—one that involves their taking care of a business associate who’s endangering not only his success but his very freedom. The boys wrestle with their consciences, especially Terry, and the outcome takes a self-destructive turn.

The actors, as usual in Allen films, give the material their all, especially Farrell, who has the most emotionally demanding role, and Wilkinson, who makes the transition from smoothness to near-hysteria ably enough. McGregor is more subdued but effective, and newcomer Atwell brings an appropriately cold demeanor to the part of an ambitious and calculating young woman. But from the technical point of view the picture is at best average, with Vilmos Zsigmond’s cinematography surprisingly bland, particularly in a long sequence in which the brothers stalk their quarry. And Philip Glass’s score—a departure from the director’s usual musical choices—is one of the composer’s more disappointing efforts, too obtrusive and insistent by half.

“Cassandra’s Dream” doesn’t sink, but neither does it soar. It’s middle-grade late Allen, which means watchable but little more.