The Ghoul Squad receives a call for help from Treesa Thrornwillow, whose sister is plotting to destroy the Haunted Garden where they both live. The ghouls must take flight with new butterfly wings to stop Treesa’s sister and save the garden.
The Ghoul Squad invite Venus to join them in a late night sleepover. Cleo boasts that she intends to stay up all night long, but at the sleepover, ends up falling asleep.
Suddenly a ball of light touches a flower in a vase, and a ghoul's face appears in it, calling to them. Venus recognises it as Treesa Thornwillow, an old friend of hers who looks after an enchanted garden. Treesa is calling because her sister, Thorna, is acting strangely. The two of them have looked after the garden together for hundreds of years, but Thorna has taken off and spoken about making the garden disappear. The Ghoul Squad and Venus offer to investigate.
The ghouls teleport to the garden, where they find Thorna and some bee ghouls creating some strange pollen. Venus recognises it as red pollen, which can disintegrate any plant life it touches. Suddenly, Thorna spots them and traps them in a cage of vines, stealing the Mapalogue from them.
Back at Monster High, Gil has created a zen garden in order to indulge in some meditation. Abbey sees this and thinks meditating looks silly, but Gil invites her to give it a try. She sit down and tries it, and soon finds herself relaxing. However, this causes her to create a cold breeze which gives Gil the chills. Deuce comes along, and the two invite him to try meditating too. However, Deuce's idea of meditating is to beatbox an annoying tune out loud.
In the garden, Draculaura escapes the cage by turning into a bat, and grabs some of the red pollen to make a hole for the others to escape. Thorna spots them and recaptures Venus while the others plummet down a large tree. Luckily, they are saved by Treesa. After they tell her about the red pollen, Treesa decides it's time to use her own pollen to even the score. She blows some magic pollen onto the Ghoul Squad, which bestows them with wings and the power to fly. With their new powers, the ghouls fly back and fend off Thorna's bug minions, before flapping their wings and blowing the red pollen into a lake.
The ghouls confront Thorna, and she admits that she had grown tired of staying in the garden forever, and wanted to explore the world beyond it. Treesa gives her her blessing to leave the garden, and gives Thorna a set of wings. Thorna is worried about leaving Treesa alone to defend the garden, but Treesa assures her than if she needs help, she can call on the Ghoul Squad.
The Ghoul Squad return to Monster High, where they discover several students have decided to try meditating in Gil's zen garden, much to his frustration. The ghouls offer to take him to Treesa's garden, where he can finally meditate in peace.
Treesa Thornwillow and Thorna Thornwillow make their animated debuts.