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Whatever happened to Hugh Grant?

Apparently the shambling star of such ’90s romantic comedies as “Notting Hill” and “Four Weddings and a Funeral” matriculated at Hogwarts, where he was hocus-pocused into a ginger-haired lad named Domhnall Gleeson.

Gleeson played one of the Weasleys in the “Harry Potter” series and ostensibly is the son of actor Brendan Gleeson. But by the evidence in the retro romance “About Time,” he is Hugh Grant transmuted by the butterfly effect.

The notion in film and physics that time travel could produce ripple effects is too-briefly mentioned in this lightweight but likable movie. The time traveler is Tim (Gleeson), who learns on his 21st birthday that the men in his family can leap backward to points in their lifetime and undo their mistakes. Tim’s father (Bill Nighy) warns him not to monkey with matters of life and death. But in the script by director Richard Curtis (“Love Actually”), the rules of this alternate reality are brushed aside to make room for some familiar fluff.

London lawyer Tim meets American Mary (Rachel McAdams with a homely hairstyle) in a pitch-dark restaurant, but he fails to make a love connection; so he retreats to his time-travel closet, clicks his heels and conjures a do-over. He does it again to fend off a rival, and then again to refine his own lovemaking technique.

There’s a lot of comic and fantasy potential here, but much of it gets squandered. As Mary and Tim grow closer and contemplate a life together, he’s rarely inconvenienced by his “gift” — and never bothers to reveal it to his beloved.

A romance built on a mutual admiration for the model Kate Moss is pretty flimsy to begin with, and Gleeson is such a big bundle of tics that McAdams (who also co-starred in a more complicated version called “The Time Traveler’s Wife”) gets crowded out of the picture.

A subplot about the illness of Tim’s father reminds us why Nighy is such a treasure, but another one about saving Tim’s free-spirited sister (Lydia Wilson) from a bad boyfriend is just too much of a gooey thing. And a subplot about a prickly playwright (Tom Hollander) adds nothing to the movie but minutes.

We suspect that if he could do it all over again, Curtis would go back in time, trim some of the flab from his screenplay and retrieve the young Hugh Grant. It’s about time for that rascal to make a comeback.

What “About Time” • Two and a half stars out of four • Rating R • Run time 2:03 • Content Mature language and some sexual content

Joe Williams is the film critic for the St. Louis Post-Dispatch.