Most good stories start with a fundamental list of ingredients: the initial situation, conflict, complication, climax, suspense, denouement, and conclusion. Great writers sometimes shake up the recipe and add some spice.
Exposition
Fairies and Witches and Golems, Oh My!
Kendra and Seth learn that their grandparents are caretakers of a preserve for magic critters called Fablehaven. This is pretty cool… but also dangerous. Following the rules will keep them safe from magic harm, but what kid actually follows the rules all the time? As we learn about all this stuff, we're seeing the stage set for what comes next in the story.
Rising Action
Fairy Tale Gone Wrong
Seth angers the fairies and is transformed into a mutant walrus. Luckily it's fixable, but asking the witch Muriel to get rid of his tusks and such comes with a price: she's one step closer to freedom.
With the magic creatures agitated over these events, Midsummer Eve becomes even more dangerous for the humans—and if the fairies don't help protect the house, who knows what might get in and harm the people inside, like Kendra and Seth, and Grandpa? (By the way, where's Grandma? We still don't know.)
Here we're seeing a bunch of dominos lined up and ready to fall… you know, if by dominoes we mean stuff that angers magic creatures and could easily hurt you or at least ruin your day.
Climax
Black Magic Woman
Disaster strikes at Midsummer Eve: Grandpa is kidnapped and the kids are left alone. Well, not entirely alone: turns out their pet chicken is their grandmother under a curse. In asking Muriel to undo the curse, they free the witch—and she promptly disappears to do mischief.
And Muriel's mischief is no small matter: She is trying to free Bahumat, a demon that'll destroy most of Fablehaven and turn it into a refuge for darkness and chaos. Muriel captures Grandma and Seth, leaving Kendra to desperately beg for help from the Fairy Queen, even though doing so could get her killed. If that ain't a crisis, Shmoopsters, then we don't know what is.
Falling Action
Fairies in Action
Kendra's gamble works, and a fairy army assembles to imprison Bahumat again, this time with Muriel thrown in as well. The fairies disenchant everyone that Muriel transformed, and Kendra too is left changed: she can see magic creatures without having to drink magic milk daily like most humans do.
Things are almost-kinda-sorta back to normal, as we see the plot threads of Muriel's dark magic and the chaos of Midsummer Eve wrapped up, and the conflict between Seth and the fairies wrapped up.
Resolution
Back to the Mundane World
Grandpa tells Kendra that he's proud of her bravery, and he's seriously considering making her the next caretaker of Fablehaven. Kendra and Seth's parents come back to pick them up and take them home, and knowing that no one would believe them if they tell their story, Kendra and Seth bond over their Fablehaven adventures. Their time at the magic refuge is done… for now.