A young runaway orders Pop-Tarts in a diner. He reads the story of the origin of Pop Tarts from the Kellog's box it came in. Bob Cabana (Jerry Seinfeld), who is sitting next to the boy in the diner, offers to tell him the true origin story of the American breakfast food.In 1963, Bob is head of development at the Kellogg's corporation, headquartered in Battle Creek, Michigan. In this period, the American breakfast is defined by milk and cereal. The 2 undisputed giants of the breakfast world are Kellog's and Post. Kellog's is led by Edsel Kellog, and he reviews the daily sales numbers with Bob. Fruit Loops have just been launched and the survey responses are extremely bad. Time to sag 14 seconds, zero milk buoyancy, and sinking easily. Bob asks to double the sugar and triple the gluten and respell FRUIT as FROOT. After once again dominating their rival Post in the annual Bowl and Spoon Awards, Bob senses that Post is about to unveil something that could dominate the market. Post is led by Marjorie Post, and her PA Rick Ludwin (Max Greenfield). Isaiah Lamb (Andy Daly) leads Quaker Oats. Soon after, Bob observes kids' Butchie (Bailey Sheetz) and Cathy (Eleanor Sweeney) dumpster-diving outside the Post HQ. Bob gets curious and goes to investigate himself. He discovers that Post is creating a shelf-stable, fruit-based pastry breakfast food that seems to have addictive effects on kids. The kids were looking for the by-product of the production process, which itself was a sweet gooey substance, and highly addictive in itself.A spy at Post reports that they have further developed a product Bob's former co-worker Donna "Stan" Stankowski (Melissa McCarthy) had created for Kellogg's. The spy reported that Post had access to the original work done by Bob and Stan and built on it. Bob knows that no cereal would survive against the fruit-based pastry. Bob convinces Kellogg to hire Stan back from NASA, and the team sets to work creating their own version of the pastry, joining forces with several prominent industry figures as "taste pilots." The pilots include soft serve ice cream genius Tom Carvel (Adrian Martinez), Children's bicycle maker Steve Schwinn (Jack McBrayer), inventor of the sea monkey Harold Von Braunhut (Thomas Lennon), canned meatballs inventor Chef Boy Ardee (Bobby Moynihan), fitness icon Jack LaLanne (James Marsden), and a computer from IBM guided by Purvis Pendleton (Aparna Nancherla). Edsel says that they are developing a product that doesn't need milk, which is guaranteed to earn the ire of the ruthless milk syndicate which will do anything to protect its own territory.Post also interrogates the dumpster kids and realizes that their new product has already been leaked to their competition. But their product is still not complete, as it is causing rashes. Marjorie decides that Kellog's is upping is game and wants the product on the shelves quickly.Marjorie Post (Amy Schumer), the head of the Post company and Edsel Kellogg's (Jim Gaffigan) former lover, calls a meeting of the "five cereal families": Kellogg's, Post, Quaker, Ralston Purina and General Mills. To the surprise of Bob's team, Marjorie announces that their product will be on shelves within one week. Bob undercuts them by obtaining exclusive rights to 99% of the world's sugar by making a deal with Puerto Rican criminal El Sucre (Felix Solis).Bob begins to worry about the taste pilots' lack of progress, but he and Stan combine several of their ideas to come up with a rectangular, fruit-filled food packaged in foil that can be toasted. Harold and Boy Ardee team up together to create a sea monkey filled Ravioli, that comes alive. Eventually, the sentient ravioli grows and then escapes captivity. Kellogg warns Bob that by creating a product that is served without milk, they may be stepping on the toes of the dairy industry, in reality an incredibly powerful and ruthless cabal who end up kidnapping and threatening Bob. Harry Friendly (Peter Dinklage) is the leader of the milk syndicate who abducts Bob. Bob is made to walk down "the aisle", a passage in a cow shed, surrounded by cow's behinds.Meanwhile, Marjorie cannot get sugar anywhere in the world. She visits the USSR to secure rights to Cuban sugar from Nikita Khrushchev (Dean Norris). The idea of a communist breakfast worries president John F. Kennedy (Bill Burr), who summons the Kellogg's team to the White House, and agrees to instruct his brother to put pressure on organized milk.While testing the new pastry, taste pilot Steve Schwinn (Jack McBrayer) is blown up in an accident (his oxygen supply snaps and comes in contact with the heat source of the toaster, igniting it) and is buried with "full cereal honors". But the taste pilot is a success and Kellog have a new breakfast treat. Meanwhile, Thurl Ravenscroft (Hugh Grant), a long-suffering Shakespearean actor who performs the mascot role of Tony the Tiger for Kellogg's, is convinced by the milk syndicate that the new breakfast pastry will make the cereal mascot obsolete. At Schwinn's funeral, Thurl convinces the other mascots to join him in a strike.The Post sugar deal with Russia triggers the US-Soviet Cuban missile crisis. Marjorie and Edsel realize that their feud is going to destroy everything they have built. Edsel decides to release Marjorie's sugar.The team struggles with marketing the new pastry. The ad executives suggest a marketing campaign around the provocative themed "Jelle Jollie". They eventually settle on the name "Trat-Pop" (Toaster Ready Anytime Treat, Put on Plate) by consulting Butchie and Cathy. A mob of mascots, led by Thurl - now dressed as the QAnon Shaman - violently breaches Kellogg's headquarters, hoping to stop the product from being certified by the FDA. They are too late, and the product is certified. Walter Cronkite (Kyle Dunnigan), reading a news brief off a piece of Silly Putty, misreads "Trat-Pop" as "Pop-Tart," forcing Kellogg's to change the name moments before they are shipped out.The following morning, Pop-Tarts sell out of every store in the country within 60 seconds, defeating Post's poorly named "Country Squares". Thurl ends up facing a congressional committee for his role in the attack, the milkmen are implicated in Kennedy's assassination, and Marjorie Post becomes an icon of feminism who retires to Mar-a-Lago.Stan leaves Kellogg's again becomes a hippie and invents granola. Bob becomes nationally famous, and during an interview on The Tonight Show with Johnny Carson, is shot by Andy Warhol (Dan Levy), who is furious that the name "Pop-Tart" sounds like "pop art." Bob survives thanks to the titanium foil packet in his pocket.In the present, the boy expresses doubt that a Pop-Tart packet could stop a bullet and begins to question other elements of the story like the existence of a sentient ravioli creature. Bob admits that the story was made up as the boy's parents arrive to take him home. As they turn to go, the ravioli creature emerges from Bob's pocket.