Notably only for a first act that credibly depicts a three-way — and, eventually, four-way — relationship among friends and lovers without tilting embarrassingly toward titillation and/or soap opera, the blandly titled The Edge of Love is only incidentally a Dylan Thomas biopic. Welshman Matthew Rhys (currently on American television in Brothers & Sisters) plays the poet, and although the film draws on Thomas’ writings in voiceover (some of them the famous archival recordings in the poet’s own voice), he’s never the center of the drama. The film opens close in on a shot of Keira Knightley, playing Vera Phillips, a singer in a London nightclub during World War II. She meets Thomas, apparently an old childhood friend, and is charmed — but surprised when the poet’s wife, Caitlin (Sienna Miller), arrives on the scene. The three of them — starving artist, wife and, perhaps, muse — move in under one roof. Vera also catches the eye of William Killick (Cillian Murphy), a good-looking but perhaps too earnest solider who’s preparing to return to the front lines, and would like to take a wife before he goes back. She agrees, which makes Killick forever a member of this dysfunctional group.