Towards the end of the Great Egg War and beyond, the disgruntled eagle Zeta was putting together a plan to expand her frozen island resort through conquest so that it encompassed three islands and not just Eagle Island, by demolishing Bird Island and Piggy Island with a powerful superweapon that she and her eagles constructed and managed. Her initial attacks on both islands ended the war between the Birds and Pigs, drawing them into an alliance that dispatched an special forces squad that ultimately thwarted her plans.
After being spurned by her lover Mighty Eagle just before he proposed to marry her, Zeta spent years on Eagle Island constructing a frozen resort. Dissatisfied with its problems, including the ice and the constant presence of a hungry seal, she began drawing up plans to expand her living space as she raised Debbie, born out of wedlock apparently due to premarital sexual relations with Mighty Eagle. She ultimately chose to accomplish this by constructing a powerful ice ball cannon that would become strong enough to raze nearby islands, including Bird Island and Piggy Island.
After the weapon's basic functionality became operational, Zeta tested her weapon by shooting it onto the shores of both islands, effectively declaring war on both the Birds and Pigs. The attack prompted Leonard, ruler of the Pigs, to call an emergency truce to his war with the Birds that ignited over the Pigs' interest in stealing Bird eggs as food. He then traveled to Bird Island in person to convince Red to put together an alliance and a strike team to confront their new enemy, Zeta and her eagles, to save both of their homelands.
While Red and Leonard were putting together the team, Zeta ordered her eagles to target Mighty Eagle's cave next with the cannon, as a way to finally get revenge on his rejection. By the time she fired the weapon there, the team was also there discussing their plans and ended up being forced to make a narrow, harrowing escape just as the ice ball impacted the cave, destroying it altogether.
With time running out, the strike team then decided to begin their mission to Eagle Island to destroy the superweapon. While they were en route, Zeta demanded that her scientists get to work making sure the cannon could now fire lava-ice balls, more powerful projectiles that would effectively raze both islands. The strike team then arrived on the island mostly undetected, but after Red expresses discontent over not being credited on using the decoy eagle Harvey to get inside, he plans his own attack on the superweapon while the rest of the team moved on, with Silver coming with him to make sure he was safe. After Red's plan fails, the two are noticed, subdued and captured by elite Eagle guard Hank.
The rest of the team make it all the way to the cannon chamber with the disguise and distract all the guards inside with break dance moves, but are forced to hide after Chuck recklessly destroys it after being distressed over seeing Red and Silver caught. Not long after, Zeta announced to the eagles that the cannon was now ready to fire lava-ice balls to destroy both islands within ten minutes and that her vision with them was close at hand. In spite of the Bird-Pig special forces' renewed efforts to destroy the weapon, ten minutes pass and Zeta is poised to release a barrage of such deadly missiles so that she could be well on her way to making her ultimate resort, all for herself. Mighty Eagle then arrives at the island just then to try and convince Zeta to reconsider her dream, giving the team a second chance to destroy the weapon and succeeding in doing so. With everything lost in the ensuing destruction of the cannon, Zeta regretted her actions and abandoned her plans for a three-island resort, ending her invasion just as she was close to succeeding.