The sizzling embers of forbidden desire cloud the screen in "The Edge of Love," an overwrought but not entirely unconvincing attempt at a smoldering period romance movie. Blessed with an eager, rightly immodest cast and meticulous production value, "Edge" doesn't aspire to be anything more than a juicy British wartime soap opera, but when it finds delicious pockets of whispered betrayal, artistic impotency, and cherry-lipped invitation, it adds up to a convincing sit.

In WWII England, poet Dylan Thomas (Matthew Rhys) is looking to delay his military duty by providing the scripts for propaganda films, which require nothing of his talents. His frustrations mounting, Dylan takes comfort in a reconnection with lost love Vera (Keira Knightley) while keeping his feelings for wife Caitlin (Sienna Miller) at arm's length. When Vera becomes romantically involved with soldier William (Cillian Murphy), it triggers Dylan's jealousy, and as the war rages on, the foursome experience a series of tragedies and betrayals that threaten to crush their lives forever.

Written by Sharman Macdonald (Knightley's mother when the spotlight dims), "Edge" is a verbose affair utilizing Dylan Thomas and his poet legacy as a hub to spawn often ridiculously exaggerated dialogue that triggers more cringe than swoon. It's a testament to the actors that they can shape the material into a playable battlefield of broken hearts, with each performer squeezing mightily to sell often operatic expressions of longing and association, spread out across the lines of war and spite that often divide the relationships. Macdonald achieves an amber mood of yearning that's often deliriously compelling, but she's also prone to clotted lines that even a grocery aisle romance novel would reject.

This uneven quality is never fully mastered by director John Maybury ("The Jacket"), who uses the knotty language as a blueprint to build a pastiche of surreal imagery to undercut traditional WWII visuals of desaturated death and the injustice of handwritten correspondence. Maybury can certainly form a pretty picture (his close-up work with Knightley is so decadent, it should require separate admission), but there's little in the way of leadership with the feature; he's unable to make a compelling argument out of the domestic disturbances and slow-burn attraction/decomposition between the characters. In a way it feels as though Maybury was intimidated by the screenplay and Thomas's legacy, remaining in a sudsy comfort zone to avoid the greater challenge.

In the end, "Edge" is made bearable by the cast, with particular attention to Knightley and Miller, who generate an unusual energy between them that lends the film sparks it doesn't otherwise earn. It's the friendship turned rivalry between Vera and Caitlin that fuels the finest moments of the movie, with the actresses supplying stellar work as the frustrated women of the war, propelled and confounded by Welsh behavior. It's especially rewarding to watch Miller score here, reminding the viewer that beyond awful tabloid headlines stands an actress of considerable ability.

"The Edge of Love" won't add much to the puzzle of Dylan Thomas nor doesn't it elevate the wartime drama genre; it's a workmanlike motion picture that moves patiently to an expected resolution with great performances that become its saving grace.