A time-traveling love story between a man and a woman, and a father and a son, "About Time" packs a few emotional wallops into an ethically muddled tale better in its ensemble chemistry than its admittedly meandering narrative. The writer-director is Richard Curtis, he of 2003's much-adored romantic comedy "Love Actually." While he hasn't quite hit the same sweet spot here, there is enough worth caring about to overcome the plot's issues of the structural and moral variety.

Tim (Domhnall Gleeson) has just turned twenty-one when his dad (Bill Nighy) confides in him with an explosive secret: all of the men in their family have the power to travel back in time to any period of their life they wish, just by going into an enclosed space, shutting their eyes, clenching their fists, and thinking about it. He tries it out by returning to the New Year's Eve party from the night before to kiss the girl at midnight whom he had previously disappointed by shaking her hand. Using this unexplainable newfound ability whenever things do not quite go as he'd hoped, Tim eventually graduates from school and moves away from his home on the shores of Cornwall to practice law in London. When he meets publishing company editor Mary (Rachel McAdams) at Dans le Noir, a restaurant where patrons eat in complete darkness, the two of them instantly hit it off. After choosing to go back in time to alter one detail, however, he discovers his meeting with Mary now has no longer happened. Tim concocts a plan to meet her all over again, and it works. They were meant to be.

What Tim realizes as time moves on is that there are certain things in life that cannot be avoided. The sooner he learns this and embraces the pitfalls as well as the joys that come with one's everyday existence, the better chance he has at a happy, messy future. "About Time," like Tim, eventually comes to recognize this fact of life, but to get there one is asked to follow and put an active stake in a guy who is doing things that go against the laws of nature. He might love Mary, but is simultaneously manipulating her very being to suit his own selfish desires. There is a brief mention of the butterfly effect, but director Richard Curtis does not explore with quite the satisfactory depth of, say, 1985's "Back to the Future" or 2004's "Primer" what it means when one person's time-travel can affect an entire universe's reality.

Because Tim's actions are debatable for much of the length, it is important that an actor inhabit the role who is naturally relatable and ingratiating. A conventionally hunky star wouldn't do here, but someone like Domhnall Gleeson (2011's "Harry Potter and the Deathly Hallows Part 2"), who proves to be disarming but unthreatening, is just right in the part. Gleeson shares a soulful, funny rapport with Rachel McAdams (2012's "The Vow"), whose Mary is sweet and cute, but also lacking in self-confidence, but it is his later scenes with his dad, played touchingly by Bill Nighy (2013's "Jack the Giant Slayer"), where one is eventually led to drop their defenses. Tim's fleeting return to a time from his childhood is a breathtaking moment of dramatic catharsis, one that works in spite of its manipulation. The filmmaker knows exactly what he's doing.

As Tim's Mum, Lindsay Duncan (2010's "Alice in Wonderland") has far less to do overall, but gets in a few truthful strokes when she suddenly finds herself widowed. "I am so uninterested in a life without your father," she says after his death, and yet she does move on. She has to. Rounding out the central cast, Lydia Wilson (2010's "Never Let Me Go") does subtly impactful work as Tim's younger sister, Kit Kat, hiding a tortured layer beneath her cheery exterior, while newcomer Margot Robbie is instantly appealing as Charlotte, a friend of Kit Kat's who comes to stay with the family for the summer and makes an undeniable impression on Tim. He has yet to meet Mary at this point, and years later when he runs into Charlotte in London he is left to wonder why he used to think they'd be a good match.

Though "About Time" features a curious and whimsical premise—one that, oddly enough, is uncannily similar to another film starring McAdams, 2009's "The Time Traveler's Wife"—its storytelling drive is a bit on the meandering side. This is not to suggest that the movie wears out its welcome or is outright interminable, only that it is more observational in nature than one with a clear-cut three-act structure. The screenplay ebbs and flows like reality might, albeit injected with an underlying imbellishment of the fantastical variety. A little more attention to its repeated paradoxes—and the times in which there should be paradoxes, but aren't—would have made the picture's effect more lingering after the fact. While not all that memorable, it remains a warm and diverting romantic drama with finely tuned performances worth seeking out.