Although no doubt inspired by Easy Rider, Mammuth is a road movie all on its own, a bizarre comedy with a surreal atmosphere and effects which perhaps could be expected of Delépine and Kervern. Here we begin with pig abattoir worker Serge Pilardosse (Gérard Depardieu) on his last day of work: the fact that he's given a 2000-piece jigsaw as a leaving present should perhaps give an indication of what kind of film this is. The road trip starts when Serge leaves his wife Catherine (Yolande Moreau) after dusting off his old Münch Mammuth motor cycle: there are a number of his ex-employers who haven't informed the government of his employment, so he isn't entitled to a fair pension until he tracks down those papers: the satire on French bureaucracy is evident.
So a very long-haired but ageing easy rider on a somewhat poor imitation of a Harley-Davidson goes off in search of these papers, and will have little success but on the way meet a number of oddballs, such as the guy at the cemetery where Serge worked as a gravedigger: death is a feature in this film, such as the body Serge finds in the supermarket and no one seems to be concerned about: could it be that this is part of Serge's imagination? As this is very much a trip into Serge's past – the bloodied face of his first girlfriend (played by Isabelle Adjani), who died in a motor cycle accident – will appear a number of times as a ghost of his imagination.
During his road trip he meets his niece Solange (Miss Ming) for the first time in many years. She is very much an amateur sculptor of art brut, and even makes a life-size model of Serge, with an elephant for a heart and a marmoset for a penis. The young Solange should perhaps have tried to make a living out of art brut because she seems to be incapable of finding any regular employment. Is that perhaps because she says weird things in interviews, such as mentioning in one for a cleaner that she's thought of writing her CV on toilet paper in her menstrual blood, or does she just come out with that because she's resigned to never getting a job anyway? Whatever the answer, Serge also meets his cousin Pierre (Albert Delpy) soon after meeting Solange and to celebrate the reunion they attempt (with little success) to bring back their teen years by masturbating each other.
It's uncertain if Serge's metal detecting activities with his rival Benoît Poelvoorde is one of Serge's new pursuits in retirement or belong to another period of his life, but it hardly matters: the whole film is a crazy comment on the crazy nature of life, perhaps best summed up by Catherine angrily spelling out the couple's surname several times to a virtual person on the phone.