While hanging out in the living room, Lincoln hears a frantic knock at the door. He answers the door, and discovers it's Clyde, who wants to tell something urgent. He empties out his backpack, revealing three boxes of frozen food from Frosty Farms Frozen Foods. After warming up the food, Clyde stuff them into Lincoln's mouth, making Lincoln point out that they taste exactly like his father's lasagna, mac 'n' cheese bites, and Salisbury steak. Clyde says that there's a chance that the frozen food company that made this food stole Lynn Sr.'s recipes, but to make sure before they jump to conclusions, they consult Lisa. She instructs them to put Lynn Sr.'s food and the frozen food into a machine that will analyze them. After a few seconds, the results come in, and the results state that the ingredients in both Lynn Sr.'s meals and the frozen food are the exact same, right down to the secret ingredients being included. Realizing that they have a case to solve, Lincoln and Clyde don their Ace Savvy and One-Eyed Jack outfits.
Lincoln and Clyde arrive to Lynn's Table, and tell Lynn Sr. about the frozen food company's theft. When Lynn Sr. states that it couldn't be possible, since they would have to steal his cookbook, he discovers that his cookbook really is missing, causing him to break down crying, since that cookbook contains all of his recipes he created ever since home-ed class in middle school. Lynn Sr. describes the book as black, having food stains and saying "Property of Lynn Loud" in it. With this newfound information, Lincoln and Clyde start to interrogate.
Lincoln and Clyde proceed to interrogate Kotaro and Grant, since they believe that they're the most likely suspects due to working alongside Lynn Sr. They first interrogate Kotaro at the ATM machine, asking him where he got the extra money. He states that his great-grandma passed away, but when Lincoln and Clyde think of it as a cheap excuse, Lucy arrives and confirms that Kotaro was telling the truth. They then proceed to interrogate Grant, who is riding a bike. When they question that the bike and his sneakers are new, they ask if they gave Lynn Sr.'s cookbook to Frosty Farms Frozen Foods, and Grant states that his birthday was a few days ago (the bike and sneakers were gifts), and they were there as well.
Realizing that the two have confirmed alibis, Lincoln and Clyde realize that someone may not have given Lynn Sr.'s cookbook away, but that someone stole it. As luck would have it, the headquarters for Frosty Farms Frozen Foods is in Royal Woods so they proceed to head there. Arriving to the HQ, they attempt to let the security guard give them access, but they promptly get kicked out. They attempt to pose as plumbers, but get kicked out when the guard sees through their disguises. They attempt to pose as firefighters, but a bulge in their hose flails them out of the building. As the two try to figure out how to get in, a delivery truck arrives, and proceed to jump into some boxes. When the delivery man drops the boxes off in the building, Lincoln and Clyde jump out and proceed to follow a familiar smell. Arriving to the kitchen, they discover the woman in there using Lynn Sr.'s cookbook. Barging into the room, the two immediately accuse the woman of stealing the cookbook, but the woman doesn't know what they're talking about, since she has had the book since she founded Frosty Farms Frozen Foods. Lincoln initially denies, but when looking through the book, it turns out the name inside is not Lynn Sr.'s, but Mildred Scalise. When Lincoln also points out that the dishes in the book are the same as Lynn Sr.'s, Mildred believes that Lynn Sr. stole the recipes from her, and demands to see him.
Arriving back to Lynn's Table, Lynn Sr. encounters Mildred, and at first, the two get at each other's throats, but it turns out that Lynn Sr. actually knows who Mildred is, since she was his home-ed teacher in middle school. When the two would work together, Mildred gave Lynn Sr. some unique cooking tips, and the two proceeded to write all their recipes in their own cookbooks (which explains why Mildred's cookbook looks exactly like Lynn Sr.'s cookbook). Feeling sympathy for her former student, Mildred decides to let Lynn Sr. borrow her cookbook, and the two proceed to get to cooking to create a new dish. As a result, Lincoln and Clyde declare the mystery solved, but Lincoln questions what really happened to Lynn Sr.'s cookbook.
It turns out that Lynn Sr.'s cookbook was taken by Leni, who attempted to turn it in at the library, along with Lucy's poetry book and Lola's diary. When Lola tells Leni about how personal these books are, she tells her to come with her to return the book to their father (and the other books). This makes Leni comment that Lola is being over-dramatic, since she believes that Lynn Sr. never noticed that it's missing.
Librarian Wetta has no lines in this episode while one of the teachers pursuing Flip was uncredited.