A young shell named Marcel lives with his grandmother in a human house. The divorce of the previous owners greatly affected the tiny inhabitants: most of the family, hiding in a sock drawer during the argument, accidentally ended up in a suitcase and were sent off to an unknown destination. The little one's main dream is to find his relatives, and he will be helped by an aspiring documentary filmmaker, Dean, who decides to make a story about the little ones.

“Marcel the Shell with Shoes On” is a film whose first drafts were born back in 2010. It all started when young writer and actress Jenny Slate, together with her friend and director Dean Fleischer Camp, decided to shoot a few videos about the little one in bright pink shoes and post them on YouTube. The short films quickly found their audience, later becoming the foundation for a children's book series.

Eleven years later, a feature-length film about the character is released, shot in the style of a mockumentary using stop-motion animation. The genre choice is explained not only by the desire to stay true to the original but also by an attempt to show in more detail the familiar world through the lens of a tiny shell. The first half of “Marcel” is an interview in which the journalist asks the child about the specifics of his daily life. Riding in a tennis ball, watching a favorite TV show with his grandmother, and participating in the filming of a documentary create a picture of a carefree childhood, making viewers feel a sense of nostalgia.

The autobiographical nature of “Marcel” lies not only in the script, which is built on the filming of a documentary project, but also in the main characters, played by the creators of the character. By bringing the on-screen world closer to reality, the authors paint a credible portrait of a filmmaker who decided to share his own passions but unexpectedly found popularity on the internet. “Marcel” becomes a statement that in the modern world, almost anyone can make movies, provided they have an original idea and quality equipment.

The creators also show a number of drawbacks to fame. Despite the fans’ admiration, Marcel never receives help from his followers in finding his relatives. Having learned about the creature's place of residence, the admirers start taking photos near his house and making noise, disrupting his peace. The little boy has to quickly move away from his old beliefs about goodwill and understand that the world is not limited to his home and its immediate surroundings.

A key character is also Marcel's grandmother—the woman with whom the child spent most of his childhood. An unexpected deterioration in the old woman's health occurs at the most inopportune moment: the creators of the beloved family TV show offer to film an episode about the grandson. The fear of losing his close relative presents the child with a dilemma: to agree to the filming, letting strangers into his home, or to wait until grandma's health improves. The second half of the film is a social drama about the important life choice of a child who does not feel safe on his home turf.

The old lady, in turn, tries with all her might to get the child on TV, because she understands that this is the only way to reunite with family members. It is the correspondents from the “60 Minutes” program who fulfill the little one's wish, bringing relatives together under one roof. However, the reunion does not happen without losses. With the film's finale, the creators emphasize the importance of spending time with loved ones, hinting that family communication is the surest way to let go of past events.