About Time Domhnall Gleeson, Rachel McAdams, Bill Nighy. Directed by Richard Curtis. Rated R. Opens Friday.

As a time-travel movie, About Time makes for a decent romance. Writer-director Richard Curtis, known as a romantic-comedy powerhouse for a series of hit screenplays (Four Weddings and a Funeral, Notting Hill, the Bridget Jones movies and Love Actually, which he also directed), isn’t really interested in the mechanics of time travel or in parsing the paradoxes that arise from messing with the past. He’s not even really interested in following the simple rules he establishes when he reveals that Tim (Domhnall Gleeson), like all the male members of his family, is able to travel back to past events in his own life.

Tim’s opening voiceover asserts that his story is all about love, which isn’t surprising for a Curtis movie, and indeed Tim uses his time-travel abilities to get the most out of his personal relationships. Mainly that means romancing and marrying perky American Mary (Rachel McAdams, playing another time traveler’s wife after her role in The Time Traveler’s Wife), although he also bends the space-time continuum to help out his amiable father (Bill Nighy, a highlight as always) and his troubled sister (Lydia Wilson).

Tim and Mary’s romance rides on the chemistry between the leads more than any convincingly written connection, and McAdams admirably enlivens a rather one-note character. Curtis succeeds more at the early comedy than the later melodrama, although he maintains a relatively light touch throughout. About Time is eventually undone both by the flimsiness of its own sci-fi conceit and by Curtis’ struggle to build fully realized characters other than Tim. Tim may have love for everyone, but the movie only has love for him.