As a follow-up to his beloved indie "Once," writer-directed John Carney has played to his strengths: exploring a relationship between two music-centric characters, using songs as emotional touchstones, focusing on a sure sense of character and place. The setting here is New York City, and the leads are a songwriter thrown off balance when her now-famous boyfriend dumps her - and a fired record executive who has descended into drunken self-destructiveness. A squinty, disheveled Mark Ruffalo walks the tightrope of playing this out-of-control character who the audience can still root for. A light, witty Keira Knightley charms, although her vocals are too wispy, even for her "I'm just a songwriter" character. The tunes, created by New Radicals lead singer Gregg Alexander with a number of co-writers, are a mixed lot, with some significantly stronger than others. (You'll be singing "Lost Stars" as you leave the theater.) Most transporting scenes: when Ruffalo imagines an acoustic performance expanded into full instrumentation and when the characters record songs, live, outside at different city locations - it looks like such fun, it makes you want to run out and join a band. I do wish, though, that there was more of James Corden, as Knightley's quietly amusing musician pal. And, wait, can that be Paul Romero - a regular at Colonial Theatre's Westerly Shakespeare in the Park productions - playing a bartender? Why, yes, it is.

- KRISTINA DORSEY