Plot

Mark is a middle-aged man who has spent most of his life with a mustache on his face. He suddenly decides to shave them. When he tells his wife, he disagrees with her, but.

Marc is sitting in his bath one morning and asks his wife, "how would you feel if I shaved off my mustache?" She doesn't think it's a great idea, for the 15 years they've been married, she's never known him without his 'stache. He shaves it off anyway, but when he sees his wife, she doesn't notice, neither do their friends at dinner that night, neither do his co-workers. Marc finally flips out, shouts at everyone, tells them he's tired of their little joke, and what do they really think. His wife and co-workers are appalled, what is he talking about, he's never had a mustache. In fact, he's imagining other things as well, or is he?—poco loco

This synopsis is especially detailed in the hope that it will help interpret this enigmatic film.

La moustache starts with a view of waves in darkness. The first words, in darkness, are "What if I shaved my moustache off?" Now, we see Marc (Vincent Lindon) shaving, and his girlfriend Agnes (Emmanuelle Devos) responds "I don't know you without it". She leaves, and he submerges in his bath water for a moment. Only then is there music as background to his shaving the moustache and thoroughly washing it down the drain. Later, there is a ring, and he starts for the door. She comes in asking "why didn't you let me in?". He waits in vain for her to notice his clean lip. Instead, she says he hasn't commented on her "tarty look". They drive to their friends Serge (Mathieu Amalric) and Nadia's (Macha Polikarpova) house, and he says to go in while he parks. Even Serge's little girl doesn't notice the missing moustache.

Marc overhears Serge call Agnes two-faced, and insists on hearing the story. About 10 years ago, Serge and Agnes (Serge's ex) spent a weekend with two other couples. Serge insisted that it was clear that Agnes arranged to hog the heat, and Agnes still adamantly maintains that she didn't. This suggests Agnes might be a liar. On their drive home, Marc says "the joke has gone far enough", her pretending not to notice he shaved the moustache. She adamantly insists "I don't understand?.

Finally in bed she yells "You know you've never had a moustache". He says she plotted with Serge and Nadia, so she phones them and they deny it. He checks their Bali trip photos which show a moustache, but she is asleep by then. Next morning, he sees her take the photos while she thinks he is asleep. He sees them later, but takes no action

Throughout the whole movie, he has proofs of his moustache but never uses them. It seems almost deliberate. Perhaps he is somehow not able to use them.

After that, he starts to grow his moustache again. He goes to work, but even the luncheon counter man does not acknowledge a missing moustache. A fellow-worker says "The advantage is we're dealing with both neophytes and experts. The message changes, but not the words and visuals. I like that idea".

Marc restarts smoking after three years. That night, he nearly attacks her and breaks down. He shows her some moustache remains, but they are beyond recognition. Later, naked in the shower, he lets the remains of his moustache go down the drain. After making love, she says "I'm not lying to you Marc. I've never lied to you" and he says "I know. That's the worst part. Should I see a psychiatrist?". Next morning, he gives up regrowing a moustache. She says "It's like freaking out when you're high. Just remember, it ends at some point. It has to end."

Later, he asks a stranger the difference between a new and old picture of him. The stranger immediately acknowledges the difference as "Oui, la moustache". He goes home and they try to relate well. She buys a green jacket for him, which he doesn't like. Their restaurant is all different. He likes it. She says it tastes odd. She feels like she is color blind or dyslexic. He promises "I'll always be here, whatever happens". She also restarts smoking. At home, his dad leaves a message reminding them of tomorrows visit. She denies they ever went to Bali.

Bruno (Hippolyte Girardot), from work, says Marc hasn't had a moustache in the last 15 years. Later, we see a clothes washer spinning. At noon, Agnes asks "Are we going to your parents". He says no, and she calls with an excuse. She then doesn't know who Serge and Nadia are, and swears Marc's father died a year ago. He points out she just said "parents" a minute ago, which she denies. As he's going for a nap, he says "Agnes, you're not going to vanish?". His nap is in fetal position, as the camera spins and fades into a clothes washer spin that stops. As he wakes, she gives him a pill.

Next, he wakes drugged to hear her and Bruno saying that the asylum people are coming to commit him. He manages to dress sufficiently, runs into the street, and grabs a cab. He tries to locate his parents house, where he was born, but can't find it (this personal inability may disprove she is simply gaslighting him). His cell phone says "parents" (not "mother"), but the number is invalid. He decoys Agnes and Bruno to his mothers house (that he couldn't find), grabs his passport, and drives to the airport.

Next stop, Hong Kong, where he walks alone among crowds. He buys a Hong Kong postcard for Agnes writing "Without your eyes, I see nothing", but keeps it in his green jacket. About to fly elsewhere, the customs man looks closely at him since the picture has a moustache. Suddenly, he changes his mind and rushes out of the airport. Now he walks alone while the crowd walks elsewhere. He sits on a seat facing differently from the crowd. The dark water comes as he naps. He wakes to snickers at him letting his seat face differently, and corrects it. Then, repeated scenes of him going through travel turnstiles, walking with the crowd, and facing the 'proper' direction. He is just traveling, never going anywhere. He tires and falls behind, losing the crowd, On impulse, he hops a boat to Macao China. He thinks of calling home, but changes his mind and throws his cell phone in the water.

In Macao, he wanders into a dingy hotel, and vegetates there. Scenes of an old man and even a dog also vegetating. He still won't send the postcard. He has grown a beard and moustache.

One day, Agnes shows up in his room at the Macao hotel. She has made herself at home, and continues a conversation like they had just seen each other an hour ago. No explanation of how she found him in this furthest corner of the world. He looks very unsure he wants to restart the relation. She asks "what's this clowns jacket" of the green jacket she insisted on buying him. He shaves his beard, leaving his original La Moustache. Friend show old pictures of them with him having the original moustache. Agnes expresses no surprise. The whole episode of him with no moustache has vanished. He throws away the postcard.

That night, she says "I almost thought you'd shave your moustache off earlier. I'd like to see you without it one day". He does shave it off, and she acknowledges it this time, immediately saying "You've done it. It's nice". She feels his bare lip, and they sleep.

We see the postcard sinking deeper into water. Marc wakes in the darkness, staring...