The episode opens with Arnold and his friends playing with water guns in front of the boarding house when Grandpa steps outside wearing an old fashioned American Army uniform. He explains to the kids that he's wearing it to honor the anniversary of "The Pig War". Years ago, the area was half American territory and half British territory with ownership of Elk Island in dispute. Things came to a head when an American farmer shot a British military officer's pig that was eating his crops and both sides went to war with the Americans emerging victorious and obtaining all of the land.
The kids are excited by Grandpa's tale and he happily tells them he signed them all up to be the American team during the annual reenactment. Arnold asks him how he was able to do that and Grandpa tells him he also signed Arnold's pet Abner as the pig being fought over. Arnold is concerned, but Grandpa assures him Abner will not be harmed and it will be fun.
Later on, the team arrives on Elk Island and meets the British squad led by Rex Smythe-Higgins and Rex III. The two sides exchange insults and the reenactment begins once Abner is covered in grease. A chase ensues all over the island, but eventually the British team captures Abner. To Arnold and Grandpa's shock, they find out that whoever captures the pig also gets to eat it. The British team takes Abner back to their fort and Grandpa tells a distraught Arnold they still have until sundown to save Abner.
Initially, Arnold goes up to the fort gate and demands Rex III give Abner back, but he's met with a barrage of rotted cabbage and fruit. The rebels then try to get into the hideout using a Trojan horse shaped like a pig. The plan works and the team attacks the Brits with water guns. Arnold makes a beeline for Abner, but gets caught as the Brits are about to cook him. Rex III refuses to release Arnold until he finds out that Abner is Arnold's pet and decides to help Arnold rescue him. The two of them use a flag to catch Abner as he's about to be dropped in a vat of boiling sauce and Abner slides happily into Arnold's arms.
As the Americans head home, Rex I is mad at Rex III for helping the enemy while Grandpa tries to persuade Arnold to do the reenactment again next year. Arnold tells him he wants to forget the whole experience but Grandpa keeps insisting.
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