Mila Starr Emily Carey infiltrates Count Dracula's castle and unintentionally wakes Dracula, the ancient master who has been frozen by the Wishbone family. The moment he stirs, Mila uses quick thinking to trap him and bring him back to her clan, where Dracula becomes a captive for the Starrs. The stakes rise as the family tasks Mila with her next mission: capture Baba Yaga. Baba Yaga, Catherine Tate, has her own plans, and Mila is about to face a trail of dark magic and shifting loyalties.
The Wishbone family crash a wedding where Baba Yaga and Renfield, Ewan Bailey, are about to tie the knot. In a swift strike, Mila abducts both witches and transports them to her family. Max Wishbone Ethan Rouse remains determined to rescue his allies, and he activates Yaga's magic amulet, a relic capable of twisting their world in the same way it did before. The amulet’s power stirs the household into a new form, turning the Wishbone clan into monsters as history seems to repeat itself.
Meanwhile, the Starr family counters Mila's mission with a fresh objective: capture Nessie, the Loch Ness Monster. Max uses the amulet to trace Mila’s path, hoping to intercept her before she can finish the task. A bold plan unfolds as the family heads to a farm where Dracula’s bat-jet is kept, climbing aboard to race toward Loch Ness.
At Loch Ness, Mila proves a formidable opponent, unleashing a fierce battle with her own powers and managing to shrink Nessie. With Nessie diminished and surfacing again, Max’s feelings deepen into a crush for Mila, even as she sets her sights on a new target—the snow-capped mountains to capture a yeti. The Wishbone crew sprint after her onto the jet, chasing through the cold air toward the remote peaks. A friendly yeti appears, but Mila’s magic shrinks him in the blink of an eye, leaving the family to pick up the pace.
Fay Wishbone, Jessica Brown Findlay, gives chase and triggers an avalanche with her powers, threatening everyone on the slope. Mila escapes the blast while the family slides down toward safety, only to find Mila perilously close to the edge of a sheer cliff. Max steps in and saves her, the moment rekindling something tender between them. Yet Mila returns to her family’s side, and she refuses to capture the final, most dangerous monster. The Starrs haul Mila to the highest point of their headquarters, where monsters are kept in waiting, and after a tense moment, Mila agrees to take on the final creature.
Max uses the amulet again to gauge Mila’s next destination, guiding the family toward Tora Tora. When they confront Mila there, a towering gorilla named King Conga emerges. Mila cannot shrink the giant, but the beast seems friendly. As Conga roars, the family plays music to pacify him, and for a moment, it seems like Mila might reconsider her mission. But her focus remains on the final challenge.
Back at headquarters, a shocking plan unfolds: the captured monsters’ powers are injected into a clone of Mila. The Starr family reveals that Mila herself is not part of their plan, and the clone—Mila 2.0—receives orders to erase the original Mila. Tearfully, Mila flees the Starrs, seeking shelter with the Wishbone clan, who reveal that the Starrs are corrupt and that Mila herself has been disowned.
Mila 2.0 tracks down the original Mila, and a dramatic confrontation erupts. The Wishbone family activates the elevator to reach the highest part of their fortress, while Mila 2.0 pursues. The clone defeats the original Mila in a brutal confrontation, and Max intercepts the situation, teleporting the trio toward the highest headquarters—only for the amulet’s power to wane amid doubt. The descent into chaos continues as the elevator becomes the battleground.
In a rapid turn, Mila 2.0 assaults the family, and the others are forced to return to normal as the bats reveal a shrink ray. Max distracts the Starrs with a dance, the bats arrive, and Max seizes the shrink ray, aiming for Mila 2.0. Instead, he accidentally shrinks the Starr family and shatters the headquarters in a flurry of magic and gears. The Wishbone crew work to free the imprisoned monsters as destruction ripples outward and the Starr-copter flees into the sky.
With Mila 2.0 finally contained, the original Mila is also shrunk, and Dracula escapes with a vow to return, only to be dwarfed by Max’s quick reflexes. The collapse of the headquarters rattles everyone, Conga’s weight shifting the fortress toward ruin, forcing the Wishbone family to flee. Max and Mila manage a daring rescue to free Mila 2.0, and Mila saves Max as Mila 2.0 blinds the original Mila, leaving Max to guide Mila’s control.
In the final moments of upheaval, Mila 2.0 is crushed beneath the Starr-copter’s path as the building crumbles, but the bond between Max and Mila holds strong. As the dust settles, the remaining heroes regroup and celebrate a new balance, watching Yaga and Renfield's wedding from a distance, and quietly acknowledging that their world has changed forever, for better or worse, but with a shared sense of hope and new beginnings.
