"Plunder Island" (published in 1933) is a major Thimble Theatre storyline. The tale takes Popeye on a dangerous adventure where he must face all manner of foes, from pirates, to witches, and even monsters, in order to reach the fabled island of treasure, Plunder Island.
The story begins in Popeye's newly acquired restaurant from the last storyline, where he is informed by Wimpy that a rough-looking fellow has come to see him. Upon meeting the rough sailor type, he and Popeye immediately begin punching and harming each other in several ways, much to shock of those present, including Wimpy and Olive. Olive then asks Wimpy to go seek help from the police to break up the fight, but as soon as Wimpy leaves, Popeye and his "opponent" happily shake hands and Popeye reveals that the rough-houser is actually his old friend and former crewmate "Salty" Bill Barnacle from 20 years earlier, and that their brawl was actually the secret handshake of their old brotherhood, the Sea Dog Club. Meanwhile, Wimpy manages to find a team of police officers and has them follow him back to the restaurant to stop the "fight", but, once they arrive, the policemen are less than pleased to see two fellows happily getting along rather than fighting, and quickly plan to arrest Wimpy for misleading an officer. Yet Wimpy is able to convince the lawmen to not arrest him by inviting them to a duck dinner over at his place as an apology, while leading them outside, much to their delight. Back inside the restaurant, Barnacle Bill explains his reason for visiting Popeye, telling him that he may have found the secret location of Plunder Island and that if they joined forces, they could get their hands on all manners of priceless pirate loot, from gold to rubies to pearls the size of eggs. Popeye eagerly accepts the invite and teams up with Bill Barnacle, having become bored with the simple life of a restaurant owner and craves to go out to sea once more. Back outside, Wimpy has fled from the officers after telling them that they should bring the duck, much to their anger, and they go in hot pursuit of the moocher.
The next day, Popeye and Salty returned from a fun but violent night on the harbor where they enjoyed all manner of drinks and fights, defeating some 27 bruisers over at Mike's Place in a single night. When they returned to Popeye's restaurant, Olive told them that the police had arrived with the intention of arresting Popeye and Bill for their destructive antics the previous night. Popeye and Bill gladly turned themselves in, but not without making several sarcastic quips. Once they were placed in their jail cell, Popeye noticed a strange fellow quivering in the corner. Bill Barnacle realized that the fellow was none other than Professor Cringly, his "key" to finding Plunder Island, whom he had found at sea before reuniting with Popeye. Bill then questioned Cringly as to why he was in jail, only for the scaredy professor to confess that he purposely got himself arrested by throwing a brick through a window; he had done so believing that he would be safer in police custody while Bill Barnacle was out. Popeye proceeded to interrupt their conversation by asking if they should escape now that it was dark, but Cringly quickly begged to stay, claiming that his old mistress, none other than the wicked Sea Hag, had found him and was in the port, having supposedly seen her ship through a window. Popeye however was quick to dismiss Cringly's notions. Having past experience with the old witch, Popeye knew that she would never dock at any port in the civilized parts of the world. The trio then broke out of their prison cell with relative ease by breaking down the wall, and made their way back to Popeye's restaurant for rest and to see if anyone else had claimed to have seen the Sea Hag.
Unbeknownst to the adventurous group, the Sea Hag had been keeping track of them all from the beginning while aboard her ship, where she and her first mate Skom plan their next move to take back Professor Cringly. As Skom gives the latest details on Cringly's whereabouts to the Hag, she decides to take direct action and has Skom stay with the ship whilst she heads to port, despite Skom's protest that he should accompany her. The Sea Hag rejects his notions, claiming that she needs no guards, but she will not go alone, as her mightiest slave will be accompanying her to make sure that no one stands in her way. For this slave is a creature so terrible that even Skom would be frozen with fear at mere sight of it.
Back at Popeye's restaurant, Popeye escorts Cringly to his room for the night while he and Bill plan their voyage. They are soon joined by Wimpy who politely introduces himself to Bill in hopes of mooching a hamburger meal from him, but Popeye intervenes and has Wimpy stay Cringly for the night to help him get to sleep, doing so by telling the cowardly professor bedtime stories, which only help to make him more unnerved. Meanwhile, Popeye and Bill discuss what to do about the Sea Hag, with Popeye mentioning his last encounter with her years ago. However, their discussion is quickly cut short as they see a towering ghost-like creature staring at them from the restaurant's doorway, much to their horror. They then proceed to go after the beast, but it quickly disappears.
The two remain befuddled and horrified as they recall its ghastly appearance which reawakens unpleasant memories within the two sailors of one of the darkest moments in their youth when they were sailing together aboard the dear ol' Mary Ann. They then recall the events of that dark night 20 years ago. On that dark fated night, their ship began rigging in an ominous and unusual tone not unlike the sound of bones and skeletons moving when suddenly the moon became blood red. The two horrified sailors could only look on in horror as they saw numerous indescribable beasts clinging to the side of the Mary Ann that were led by a sinister being who left the helpless youths paralyzed. The next morning, the duo and their skipper awoke to find five of the crew missing with no trace of them left behind. All that is known is that their frightening encounter aboard the "Ol' Mary Ann" would forever remind them of the all-true horrors and evil spirits that exist within the seas.The duo quickly decided to confront their fears and find the ghostly beast, who strangely reminded them of the evil beasts that attacked the Mary Ann so long ago. They then see a very disturbed Cringly walking out of the restaurant muttering to himself about the moon and sensing that "one of them is near" while seemingly being compelled to walk into the sea, but he is stopped by Popeye and Bill who call Wimpy to take Cringly back to bed for his own good. Unbeknownst to them, the Sea Hag's glare is indeed upon them and watching their every move and waiting for her chance to strike. Back inside, Wimpy tells Cringly the story of The Woolly Worm and the Ladybug, which ends with the Woolly Worm scaring the Ladybug with a ghastly "BOO!" which frightens Cringly so much that he breaks through the roof and goes up a tree. As Popeye scolds Wimpy for his goof, Cringly is seen staring into the sea where he sees the sight of the Red Moon which is then followed by the sight of the Sea Hag's cursed ship, the Black Barnacle, causing Cringly to shout out in terror. Popeye and Bill then run outside and see the cursed sight themselves while hearing the eerie cackle of the Sea Hag. With tensions high, the duo realize that this night will be a very challenging one indeed.