Bliss is a middle-grade fantasy about a family of magical bakers.
The story opens with a prologue set two years before the main events. Ten-year-old Rosemary (Rose) Bliss watches her mother, Purdy, drive to the top of a hill during a fierce storm and capture lightning bolts in a blue mason jar. Purdy folds the lightning into cake batter and bakes a glowing loaf, which she feeds to six-year-old Kenny Calhoun, a local boy who has been in a coma after being electrocuted. Kenny revives immediately. Rose confirms what she has long suspected: Her parents are kitchen magicians who use their bakery, the Follow Your Bliss Bakery, to quietly help the people of Calamity Falls.
Two years later, 12-year-old Rose is a dutiful but overlooked member of the Bliss household. While her parents use magical ingredients to solve local crises, Rose is relegated to running mundane errands. She sees herself as ordinary compared to her handsome 15-year-old brother, Ty; her funny nine-year-old brother, Sage; and her adorable three-year-old sister, Leigh. When a neighboring mayor arrives to beg Purdy and her husband, Albert, to bake curative pastries for a flu epidemic, the parents agree and prepare to leave. Before departing, Albert leads Rose into a hidden room behind the walk-in refrigerator, opened by a whisk-shaped key. Inside, on a wooden podium, is the Bliss Cookery Booke, an ancient leather-bound volume of enchanted recipes passed down through the family. Albert gives Rose the key and strictly forbids her from opening the room or using any magic. Rose is crushed, feeling her years of dedicated service have earned her the right to try real baking.
Soon after, a glamorous young woman named Lily rides a black motorcycle into the driveway and introduces herself as "Aunt Lily," a distant cousin descended from Albatross Bliss, an ancestor from a separate branch of the family. She shows Rose a ladle-shaped birthmark identical to the one every Bliss family member has. Rose recalls overhearing her parents refuse a visit from someone named Lily years earlier, but she lets Lily stay because the bakery needs help. Lily quickly charms the household, cooking elaborate meals, managing Leigh effortlessly, and telling Rose she has untapped gifts. On her first evening, Lily serves the family a shimmering, rainbow-layered tart. After eating it, neither Ty nor Rose can speak about Lily when talking to their mother on the phone, though they do not yet understand why.
The siblings argue about showing Lily the Cookery Booke. Rose devises a compromise: They will secretly copy recipes into a notebook and practice them without revealing the book. Rose and Ty attempt Love Muffins, hoping to bring together Mr. Bastable, a shy cabinetmaker, and Miss Thistle, Rose's biology teacher. While searching for ingredients, Ty discovers a hidden cellar beneath the refrigerator filled with blue mason jars containing magical items. They bake the muffins using an egg from a Masked Lovebird, but they miscalculate the archaic measurements and produce no visible result. Disappointed, Ty loses interest and admits he gave the leftover muffins to girls in his class.
Next, Rose and Ty bake Cookies of Truth, requiring the sleeping breath of someone who has never lied. They collect Leigh's breath in a mason jar and bake 10 trays. When Rose oversleeps the next morning, the family's kitchen helper, Chip, gives a free cookie to every customer. Rose discovers that a footnote in the recipe warns the cookies must be served with milk; without it, they unleash all socially restrained honesty. Chaos erupts across Calamity Falls. Librarians storm the bakery hurling insults. Mr. Bastable, under the combined influence of Love Muffins and Cookies of Truth, publicly declares his love for Miss Thistle from atop a fake Eiffel Tower at a local restaurant. Dozens of girls from Ty's class, having eaten both muffins and cookies, mob the bakery in a frenzy over Ty. Meanwhile, Leigh eats leftover cookies and begins shouting the family's secret: They have a magical cookbook in the fridge.
Desperate, Rose searches the Cookery Booke and finds a section labeled "Albatross's Apocrypha," containing recipes from the darker branch of the family. She selects the Turn-Around-Inside-Out-Upside-Down Cake, hoping it will reverse everything. The recipe requires tears from a Warlock's Eye stored in the cellar. While retrieving it, Rose hears a sinister voice from beneath the floor offering her beauty and fame, but she resists. She bakes the cake, feeds it to Leigh, and distributes slices to everyone in town. By the next morning, however, the townspeople are walking backward, talking backward, and performing their routines in reverse. The cake turns everything inside out rather than undoing the earlier spells.
Rose has earlier given Sage the library key for safekeeping after refusing to hand it to Lily directly, but Sage has now given the key to Lily. Forced to accept Lily's help, Rose watches as Lily opens the Cookery Booke and finds the recipe for Back-to-Before Blackberry Torte, created by their ancestor Filbert Bliss to undo Albatross's original Upside-Down Cake. The recipe requires the whispered secret of time from a Dwarf of Perpetual Sleep stored in the cellar. Rose and Lily wake the cranky Dwarf and bake the torte. To distribute it, Rose exploits the backward logic of the spell, announcing there is no party in the town square and posting signs telling people not to eat the cake. The backward-thinking townspeople rush to the square, devour the torte, and gradually come to their senses. Rose bakes a final small portion for Leigh, restoring her sister to normal.
That evening, Lily proposes that Rose leave her family and come to New York to work on Lily's television cooking show. The plan requires taking the Cookery Booke. To prevent the family from noticing, Lily has prepared Forget-Me Biscuits that will erase all memory of Lily, the book, and Rose. Rose is deeply tempted; she has spent the week feeling invisible, and Lily's praise has made her feel important for the first time. She initially agrees and packs a bag.
Before dawn, Rose encounters her siblings, who ask her to help make breakfast for their returning parents. Leigh snaps a Polaroid of the four of them. Downstairs, Lily tells Rose to leave the photo behind because pictures interfere with the biscuits' magic. Rose's resolve crystallizes: She throws the biscuits into the garbage, retrieves the Polaroid, and tells Lily she cannot leave her family or steal the cookbook. Lily drops her charming facade, calls Rose nothing without her, and speeds away on her motorcycle. Rose leads her family to the library and unlocks the door to find the podium empty. The Bliss Cookery Booke is gone.
When Purdy and Albert return, they reveal that Lily tried to steal the book once before, when Ty was a baby. The children struggle to explain what happened because the shimmering tart Lily serves them on her first night is a Hold-Your-Tongue Tart that magically prevents them from speaking her name. Only Leigh, who has barely tasted the tart, can say "Aunt Lily." Under the force of their extreme fear, the tart's hold eventually breaks, and Sage spills the entire story. Rose tearfully apologizes, explaining she wanted to prove she could be a magical baker worthy of her parents' respect. Purdy reassures Rose that she is the most clever and talented person in the family. Comforted by her parents' love, Rose declares she is going to get the cookbook back. The novel closes with the Bliss family gathered at the kitchen table, laughing together over scrambled eggs, as Rose resolves to recover the Bliss Cookery Booke.