Its title promises a vaguely soap opera approach to the literary biopic. If only “The Edge of Love” were that much trashy fun.

Instead, this look-in on the life of Dylan Thomas takes the arty approach. It’s got a swell cast and some eye-filling locations in Wales, but the overall effect is exasperating.

The time is World War II, when Thomas (played by Matthew Rhys) stayed on the homefront because of his unsteady health. As the movie opens, a childhood friend, Vera (Keira Knightley), runs into him in a London pub.

Sharing their long-past romance and a Welsh heritage, they bond under the watchful eye of his wife, Caitlin (Sienna Miller), a bohemian sort with a flexible view of her own marital fidelity.

The film tries to locate its emotional center in the understanding that grows between the two women, although this is rarely convincing. Vera is single-mindedly pursued by a soldier, William (Cillian Murphy, of “Batman Begins”), whose creepy attention she eventually gives in to.

When he’s off to the war, the other three leave for the Welsh seaside, where a variety of dull antagonisms play out. Betrayals are woven in with Dylan Thomas’ bouts of drinking. Every once in a while there’s a voiceover of some beautiful Thomas poetry to remind us that the infantile character portrayed on the screen was actually a great artist.

Some of the story is rooted in truth; producer Rebekah Gilbertson’s grandparents were the real Vera and William. How much fact is contained in the script by Sharman Macdonald (Keira Knightley’s mother) I don’t know, but one imagines these people’s lives must have been more interesting than this.

The cast is the main draw. Murphy has an impossible character to play and hasn’t figured out a way to do it. Rhys, from the TV series “Brothers &Sisters,” does a nimble job of suggesting a certain escape-artist quality to Dylan Thomas, and he’s got the charm to carry it off.

Both Knightley and Miller labor hard to keep it real, but director John Maybury (who worked with Knightley on a dismal film, “The Jacket”) doesn’t do them any favors.

This film is happiest when Dylan Thomas is lying in a puddle of urine in the street outside a pub. Which is probably some kind of reality, but perhaps not the whole truth.