The novel introduces Hannah Swensen, owner of The Cookie Jar, a bakery and coffee shop in the small Minnesota town of Lake Eden. Hannah lives alone with her large orange tomcat, Moishe, and her mornings begin early with baking, fielding phone calls from her matchmaking mother, Delores Swensen, and driving her candy-apple red Suburban to work. Delores is determined to marry off her eldest daughter and has recently arranged a dinner to introduce Hannah to Norman Rhodes, a balding dentist and the son of Delores's neighbor. Hannah's 19-year-old assistant, Lisa Herman, who stayed in Lake Eden to care for her father, Jack, who has Alzheimer's, helps run the business.
One morning, Hannah's sister Andrea Todd, a real estate agent married to Winnetka County deputy sheriff Bill Todd, drops off her four-year-old daughter, Tracey, at the shop. When Ron LaSalle, the well-liked local dairy deliveryman and former star high school quarterback, fails to make his usual delivery, Tracey mentions she saw his truck turn into the alley and heard a loud bang. Hannah investigates and finds Ron dead in his delivery truck with a bullet hole in his chest and one of her cookies still clutched in his hand.
The murder transforms The Cookie Jar into the busiest spot in town. Bill, who has just passed his detective's test and been put in charge of the case, interviews Hannah and asks her to keep her ears open. A successful outcome could earn him a promotion, and Hannah agrees to serve as his unofficial undercover agent.
Hannah's first lead comes from Edna Ferguson, the school cafeteria worker, who found two coffee cups that morning, one bearing bright pink lipstick. After climbing into the school Dumpster to retrieve the discarded cups, Hannah and Bill trace the lipstick through local cosmetic sellers to Danielle Watson, wife of high school coach Boyd Watson.
At the mayor's fundraiser, Hannah confronts Danielle with the lipstick evidence. Danielle admits she was with Ron but insists they were not having an affair. Ron was her sponsor in Gamblers Anonymous. The previous evening, a check from her mother triggered the urge to gamble, and Danielle drove to the Twin Pines Indian casino. Ron found her there, stayed up all night with her drinking coffee, and then took her along on his early-morning delivery route. Danielle also mentions Ron cracked a tooth fighting a casino bouncer, explaining why Hannah had seen him cupping his jaw that morning. Hannah promises to keep Danielle's identity secret.
Hannah methodically eliminates suspects. Norman treated Ron for the cracked tooth early that morning, with Delores as his next patient, giving Norman an alibi. While Hannah lunches with Norman, Andrea snoops through his storage room and finds Polaroid photographs of bare female torsos taken in the dental chair by Norman's late father. The sisters destroy the pictures to protect the women's dignity. Coach Watson's alibi is established when Hannah overhears his sister, Maryann, describe accompanying Boyd to the Mall of America on Tuesday evening and staying overnight at his mother's house. At the Twin Pines casino, the bouncer who fought with Ron is also cleared because his wife went into labor that night. Hannah is now out of suspects.
New developments emerge at the Woodleys' annual party, hosted by Del Woodley, the wealthy owner of DelRay Manufacturing, and his wife, Judith Woodley. Hannah attends with Norman and notices Del looks haggard. His son, Benton, has returned home, claiming he wants to help with the business, though Andrea warns that Benton showed a telltale lying habit. Hannah pulls Danielle aside and learns a critical detail: When Ron ducked back into the dairy at about 6:15 a.m. to grab promotional pens, he saw the dairy's owner, Max Turner, in his office meeting with someone, even though Max was supposed to have already left for a convention in Wisconsin.
Hannah and Andrea learn that Max never arrived at the convention. Betty Jackson, Max's longtime secretary, confirms he has not called in, which is unprecedented, and reveals that Max was a ruthless businessman who made personal loans to townsfolk and foreclosed on their properties for profit. That night, the sisters drive to Max's house, find his Cadillac half-packed with his wallet still inside, then proceed to the Cozy Cow Dairy. In the old preserved dairy behind Max's office, they find the safe standing open and, behind a shelf of file boxes, discover Max's body with a bullet hole in his chest.
Hannah forms a theory: Ron was killed because he saw Max meeting with the killer at 6:15 a.m. After shooting Max, the killer checked Ron's posted delivery schedule, tracked him down, and silenced him. A call to Mr. Harris, Andrea's real estate client who was near the dairy that morning, confirms that a small black compact car with a rental sticker sped out of the dairy's driveway at about 6:45 a.m.
Examining party photos Norman developed, Hannah spots a Compacts Unlimited rental folder in Del Woodley's den. Delores reports that Del's expensive ring is for sale at a jeweler's, suggesting financial trouble. Hannah's neighbor Phil Plotnik, a night supervisor at DelRay Manufacturing, confirms the business nearly collapsed four years ago and that he saw Del at the plant at 6:15 a.m. on Wednesday, giving Del an alibi. Betty confirms Del had a personal loan from Max. Hannah clears Boyd Watson by calling Dr. Frederick Holland at The Holland Center, who confirms Boyd had a 7:00 a.m. anger management appointment on Wednesday. Upon visiting Danielle, Hannah finds her with a black eye and handprint-shaped welts, revealing that Boyd physically abuses her.
Hannah drives to the Woodley mansion with cookies, intending to investigate. Judith explains the rental car belonged to the party staffing service and produces Benton's airline tickets showing he landed at 12:17 p.m. on Wednesday, clearing him. When Hannah mentions Del's loan from Max, Judith pulls a gun and confesses. Max was about to foreclose on the Woodley home, an exact replica of Judith's father's house that she considers her entire life. Judith killed Max to prevent the foreclosure and took the loan papers from the safe. She killed Ron because he saw her at the dairy and would have identified her once Max's body was discovered.
Judith announces her plan to shoot Hannah and dispose of the body in the lake. Hannah stalls by discussing Judith's priceless Wedgwood tea set, then claims the set is a fake. When Judith leans in to examine the maker's mark, Hannah throws the hot tea in Judith's face, tackles her, and binds her wrists with Judith's silk scarf. Bill arrives moments later, having traced Hannah's movements from a voicemail she left earlier, and arrests Judith.
Sheriff Grant promotes Bill to detective and partners him with Mike Kingston, an experienced investigator newly hired from the Minneapolis Police Department. At a family pizza gathering, Hannah meets Mike and feels an immediate attraction. Norman asks her to dinner the following Friday, and Mike asks her out for Saturday. Hannah privately tells Bill about Boyd Watson's abuse of Danielle and asks him to monitor the situation. Delores, who bet Hannah that both men would ask her out, wins the wager, and Hannah honors the bet by dropping her beloved sneakers into the garbage can, ending the night with a grin and two dates on her calendar.