Late one night, Applejack and the other members of the Apple family wake to hear Granny Smith banging pans and crying out "The timberwolves are a-howlin'!" and "The zap apples are comin'!" As this isn't the first time this has happened, they know exactly what's coming, and the next morning Applejack and Big Macintosh get down to business, setting up buckets by the barren zap apple trees. Apple Bloom, meanwhile, is ready to follow Granny Smith's tutelage in making Zap Apple Jam. Granny Smith warns her that there are lots of steps to follow, and if any one of them doesn't go exactly right, the jam won't turn out right, and then hands her a broom, which Apple Bloom initially mistakes for a special part of the process. But no, it's just time for ordinary sweeping, while Granny Smith goes off to do something that she can't quite remember.
As Applejack and Big Macintosh finish setting up the buckets, storm clouds roll in, and the barren trees begin to crackle with electricity, suddenly sprouting leaves. Right on schedule, according to Applejack. Meanwhile, Granny Smith and Apple Bloom, dressed as bunnies, hop over watering cans full of water while singing the alphabet, until they're visited by Filthy Rich, Diamond Tiara's father. It seems he's there on business, having heard that the zap apple harvest is coming up, and he usually gets the first hundred jars of jam. Just four days, Granny Smith tells him, and as they head off to talk, Diamond Tiara mocks Apple Bloom for having to make jam with her granny. At first, Apple Bloom doesn't bite, since she's been looking forward to making the jam, but when Tiara points out the odd behavior of Granny Smith, Apple Bloom suddenly sees her gran in a new, more embarrassing, light.
Apple Bloom and Granny Smith head into town to pick up a thing or two, with Granny Smith wearing her dentures for the occasion. Bit by bit, Granny Smith embarrasses Apple Bloom, whether it's by biting an iron skillet to test it out or wearing a beard of bees while getting some honey. To Apple Bloom's further humiliation, Diamond Tiara and Silver Spoon happen to pass by, and her attempt to make Granny Smith act less conspicuous utterly fails.
The next day at school, Diamond Tiara's father explains how his store, Rich's Barnyard Bargains, became the cornerstone of Ponyville commerce, though only Diamond Tiara and Twist seem at all interested. It seems that they've been having a string of Family Appreciation Days, and now Apple Bloom is the only one who hasn't had a family member come and speak. But the next schoolday, Monday, Apple Bloom points out, is the day of the zap apple harvest, so Applejack and Big Macintosh won't be able to come. Diamond Tiara points out that Granny Smith would be able to come, and before Apple Bloom can protest, Cheerilee approves, and school ends for the day.
Apple Bloom tries to appeal to Applejack and Big Macintosh to come instead, but since the zap apples disappear after the fifth day, there's no way they can miss the harvest. The stormclouds blow in again, and a murder of crows come with them, forming apple shapes over the orchard. Granny Smith declares this the third sign, right on time, and sure enough, the zap apple trees crackle with electricity and their buds become blossoms. Granny Smith calls for them to get back to work, and as she heads back to the house, Applejack reassures Apple Bloom that Granny Smith will be sure to entertain the class. Which is exactly what Apple Bloom's afraid of.
After sharing her fears with the other Cutie Mark Crusaders, Scootaloo and Sweetie Belle swear to find a way to put off Apple Bloom's turn. Apple Bloom declares she's getting sick from worrying, which gives Scootaloo an idea. Meanwhile, Granny Smith lines up her jam jars and gives them a military-style review, insisting that there will be no cracking under pressure. And when one jar does, indeed, crack, it is unceremoniously court-martialed (i.e. thrown out).
During all that, Scootaloo and Sweetie Belle put Operation: Sick Day into motion by giving Apple Bloom a greenish complexion with some mashed up grapes and a high temperature courtesy of a thermometer in a tea pot. None of this fools Granny Smith, though, as she ignores the signs and just feels Apple Bloom's forehead. With that plan busted, the CMC retire to the clubhouse to figure something else out. Before they can, though, Sweetie Belle notices shooting stars, the fourth sign. And right before their eyes, the zap apple tree's blossoms turn into tiny apples. Which gives Sweetie Belle a new idea.
sneak out to the orchard to try harvesting the zap apples early. Apple Bloom isn't convinced this plan will work, since zap apples just aren't normal. But Sweetie Belle doesn't heed her warning and gives the tree a buck. The tree, in turn, sends down a jolt of electricity that sends Sweetie Belle shooting across the orchard. Their attempt to pick the apples doesn't go well, either, as the stem of the apple refuses to break, even with all three fillies pulling, and one false step sends the three of them catapulting all the way to the pig pen.
But by the next day, they've come up with a new plan: taking advantage of Granny Smith's daily nap, the CMC rig her up like a puppet and have "her" tell Miss Cheerilee that she can't possibly make it to school for the presentation. Cheerilee buys this, and hearing that their plan actually worked, Scootaloo jumps for joy, sending Granny Smith up in the air and waking the old pony up. Seeing Miss Cheerilee walking away, Granny Smith calls out to her, and affirms that yes, she will be at the presentation. Cheerilee leaves, confused. Since she's up, Granny Smith paints polka dots all over the kitchen walls, and Apple Bloom laments their plan failing, wishing she could just run away. Which gives Sweetie Belle yet another idea...
The next morning, the storm clouds return yet again, and this time their passing leaves a beautiful rainbow. The rainbow goes from tree to tree, giving each apple a set of rainbow stripes and a fuller shape. The zap apples are ready for harvesting! As Granny Smith heads back inside, she's interrupted by Scootaloo, dressed as a messenger, who hands her a telegram. This plan, to send Granny Smith out of town for the day, appears to work, and just in time! At school, Apple Bloom tells Miss Cheerilee that Granny Smith was called out of town, only for Granny Smith to show up! Yes, the CMC's plan failed, for the very relative they sent her to visit just happened to be coming to visit them!
Her family planted the zap apple seeds, and over the years, she learned the signs of the harvest and the strange behavior of the trees themselves. She also learned the special techniques needed to make zap apple jam, such as being friendly with bees, dressing down glass jars, and painting pink polka dots on the walls. It wasn't long before ponies started coming from all over Equestria just for the jam. And the first thing Diamond Tiara's great grandfather, Stinkin' Rich, sold in his store was the zap apple jam. This all lead to the town that would become Ponyville being founded.
As Granny Smith finishes her story, the class is speechless, until Silver Spoon (Diamond Tiara's crony, you may recall) starts the applause. Scootaloo points out this means the zap apples are responsible for Ponyville's very existence, and Apple Bloom needles Diamond Tiara with the fact that her granny made her father's store profitable. Diamond Tiara takes offense, claiming that Granny Smith is just a "kooky old lady," and Apple Bloom leaps to her granny's defense.
The next day, Apple Bloom helps Granny Smith make the zap apple jam, which ponies still line up for. Scootaloo declares it the best batch yet, thanks to Apple Bloom helping out, and Granny Smith agrees, to Apple Bloom's delight. Applejack rightly guesses that Family Appreciation Day went all right, and Apple Bloom apologizes to Granny Smith for being embarrassed by her. But it's all good, and all the little fillies go to help Granny Smith sing to the water, even Diamond Tiara, though she has to be pushed into it by her father.
Big Mac sniffs the wind
Watering the trees
Happy Apple Family
Kissing Celestia's Hoof
Wrong Move, Mr. Smith
Zap Apple products