Pirates of the Magical World III
Treasure Island
1996
Having escaped Azkaban once Harry's disappearance reached him (October 1991), Sirius searched for his godson fruitlessly for years. But when he was finally found, Sirius rushed to Port Royal to find and meet him. When the Great Upheaval happened, he stowed aboard a ship and later got himself hired as a deckhand. After fourteen months, his ship lands in a port that the Rogue Cutlass was in.
He found Harry discussing with Dudley his need to get a big haul so his wife could set herself up comfortably. Sirius butted in and mentioned Gringotts. With London long gone and the Magical World on the verge of a big war against the Death Eaters, the sunken bank was a treasure trove just waiting to be found. Harry and Dudley are somewhat suspicious of Sirius until he reveals himself of Harry's long lost godfather. They take Sirius as navigator and sail to London.
Once they found and entered the bank, they saw Sirius had been correct: mountains of untouched gold and silver coins! They took as much as the Rogue Cutlass could haul before sailing away. They decided to stop on an island where they offloaded their present amount of bounty and hid it in a cave, surrounded by deadly traps. Though a lot of the pirates didn't want to leave their bounty like that, they all agreed they wanted to get as much gold as quickly as possible and there was only so much room in the sloop.
They made three more trips, collecting a huge amount of gold and silver. But when they went back for the fifth trip, they were ambushed by six mans-o-war, manned by Death Eaters. Cutting their losses, the Rogue Cutlass fled but the mans-o-war pursued, wanting 'their' gold back. Despite the Cutlass's best efforts, the sloop was badly damaged, boarded, and the crew captured. The Death Eaters kept the pirates alive for 'sport' (torture), the Rogue Cutlass was sunk afterwards.
When they learned that Harry was one of them, they were ecstatic at delivering him to Voldemort. However, the Death Eaters also guessed that the pirates had already raided Gringotts and they wanted that gold. Harry was forced to take the pirates to the island they hid it on. Even with Harry's guidance, a lot of the Death Eaters were badly injured or killed.
After loading the huge amount of buried treasure into one of the mans-o-war, the Death Eaters were suddenly attacked by the Magical Britain navy who'd been tracking them for weeks. The pirates used the chaos of battle to escape the brig, swim to man-o-war with their plunder, commandeering it, and flee from the battle, leaving to two factions to duke it out.
With their recovered gold, they landed at their favorite port and divided their shares. Sirius was surprised to find himself being given his own share and be heartily welcomed as part of the crew. They may have lost the Rogue Cutlass sloop, but they got an even more powerful Rogue Cutlass man-o-war in exchange. Sirius was completely flabbergasted to meet Harry's pregnant Veela wife, Fleur.