Over the past three decades, Woody Allen has written and directed a new full-length feature almost every year. If you don’t think that excuses a poor outing every once in a while, you clearly have no idea how hard it is to make one good film. Unfortunately, Allen has been in a rut for some time, and though “Cassandra’s Dream” marks his third consecutive film to take place in London, it lacks the focus of his first (“Match Point”). The film stars Ewan McGregor and Colin Farrell as a pair of brothers with ambitious plans for the future. Ian (McGregor) dreams of becoming a big shot real estate investor, while Terry (Farrell) just wants to make a better life for him and his girlfriend. When both run into money problems, however, they look to their successful uncle Howard (Tom Wilkinson) for help. He’s more than willing to loan them the money, but first, they have to do him a favor: murder a fellow associate who plans to rat Howard out for his questionable business ethics. Much like “Before the Devil Knows You’re Dead,” Allen’s latest film is a second-rate thriller disguised as a masterpiece. Though McGregor and Farrell both deliver solid performances, the story goes nowhere due to Allen’s inability to develop his characters beyond their one-dimensional relationships. It’s too bad, because while “Cassandra’s Dream” definitely has potential as a film, it would have worked better on the stage.