Three years have passed since the Birds took decisive action against the Pigs, leaving Pig City in ruins due to their egg theft. Now, Red, voiced by Jason Sudeikis, is dedicated to safeguarding Bird Island from the retaliatory antics of the Pigs, led by the mischievous King Leonard Mudbeard, played by Bill Hader. After the reconstruction of Piggy Island, the pigs and birds become entangled in a prank war. However, an unexpected giant ice ball from Eagle Island alters the stakes when it splashes into the sea near Piggy Island, prompting the pigs to pursue a temporary alliance with the birds.
At the center of the chaos is Zeta, the cold-hearted leader of Eagle Island, voiced by Leslie Jones, who is furious over her icy domain and makes plans to seize both islands. She aims to do so by deploying her super-weapon to bombard the regions with ice balls, forcing their inhabitants into submission.
In a twist of fate, Red and his best buddies, Chuck and Bomb, surprise him with a unique speed dating event. During this encounter, Red meets Chuck's sister Silver, an astute engineering student, who quickly assesses that they're not a match. Meanwhile, Leonard persuades Red to form a temporary alliance with the pigs, enlisting Mighty Eagle, voiced by Peter Dinklage, along with Chuck, Bomb, and Silver.
As they gather in Mighty Eagle's cave, a startling intrusion occurs when an ice ball strikes Eagle Mountain, sending shockwaves through Bird Island. Determined to protect their home, the team sets out to Eagle Island via a submarine, with Red reassuring his fellow birds they are safe to stay—despite his own fears.
Upon reaching the island, Mighty Eagle reveals a haunting secret: Zeta was once his fiancée, a relationship he abandoned out of cowardice. Red initially seeks to confront Zeta alone, but is soon followed by Silver who proves to be unwavering by his side. They infiltrate the enemy base only to be captured and frozen.
While trapped, Zeta reveals her nefarious plan for an explosive assault involving ice balls packed with lava. Feeling regretful for not evacuating the birds sooner, Red confides in Silver his longing for acceptance. Yet, with her help, they manage to escape and regroup with the team. As Silver takes charge, she devises a bold strategy to dismantle Zeta's weapon.
In a fierce climax, Red and Silver place themselves in an ice ball and roll down the ammunition track of Zeta's weapon. Their teammates scramble to sabotage the mechanism to prevent a catastrophic launch. In a moment of desperation, Mighty Eagle confronts Zeta, revealing his true identity, Ethan, and the shocking truth that Debbie, her loyal servant, is their daughter.
While Zeta is momentarily distracted, Chuck employs Silver’s brilliant invention, Super-String, to secure the weapon and halt the lava balls. As the tension escalates, the teamwork between the baby birds and piglets proves essential, ultimately leading to the annihilation of the weapon and Zeta's fortress.
With all residents escaping with their lives, Mighty Eagle redeems himself by saving Debbie from disaster, mending bridges with Zeta. In a celebratory conclusion, Mighty Eagle and Zeta tie the knot on Bird Island, with Red as the esteemed witness. As the festivities unfold, he acknowledges his friends for their bravery and selflessness, cementing his beloved status among the community. Meanwhile, a budding romance blossoms between Red and Silver, heralding a new chapter for both of them amidst the joyous union.
