|“||Carrying a flashlight is better than hiding a picnic basket!||”|
— Sadie Bellamy, The End
How and when Sadie and Jonah came to the Island and why they chose to stay is unknown. It is possible that they were born on the Island, as Friday Caliban mentioned that there other children born there who were secretly taught to read by Professor Fletcher. The idea that they are children is also supported in the fact that their jobs on the island are not mentioned.
She knows of Arthur Poe somehow as she is able to correctly guess his name while talking to Count Olaf, although it is possible she knows of him because the Baudelaires may have mentioned him at an unseen time. She also knows of Erewhon's picnic basket, which she hid instead of sending to the arboretum.
- Count Olaf: The adoption papers were hidden in the hat of a banker who had been promoted to Vice President in Charge of Orphan Affairs.
- Sadie Bellamy: Mr. Poe?
While storm-scavenging the day that Violet, Klaus and Sunny Baudelaire wash ashore, Jonah and Sadie bring the boat that the Baudelaires were shipwrecked in to Ishmael. However, as the island is almost finished with its customary outrigger, they have no use for it, and they lift it onto the sleigh for the sheep to carry to the arboretum.
Sadie is among the crowd of islanders who go storm-scavenging the day the Count Olaf and Kit Snicket wash up ashore, with Kit on a raft of books. The colonists leave to go fetch Ishmael to decide what to do, leaving Olaf under the watch of Friday and the Baudelaires.
Upon returning, Sadie and Jonah lift a birdcage from Ishmael's sleigh, set it down, and open the door, glaring meaningfully at Count Olaf. After Weyden and Ms. Marlow force him into the caffe, the Bellamy siblings shut and latch the door. They later remain with the crowd of islanders, who are convinced by Ishmael to abandon Olaf, Kit and the Baudelaires on the coastal shelf.
When the island has a mutiny over breakfast, Jonah and Sadie are seem arguing face-to-face. When Jonah announces that Finn has been carrying a flashlight, Sadie retorts that carrying a flashlight is better than hiding a picnic basket, as Erewhon had been doing. Count Olaf arrives and begins to monologue, and when he mentions a Vice President in Charge of Orphan Affairs, Sadie guesses that he means Poe.
Ishmael shoots Olaf with a harpoon gun, which causes the Medusoid Mycelium to be released, poisoning the islanders. Ishmael suggests the islanders drink cordial to try and dilute the poison, and the fermented cordial drugs them into compliance. He convinces them that the Baudelaires are the root of the trouble, and then gathers them on the outrigger and has them sail off towards Lousy Lane for a cure, though they will not make it in time to save their lives.
It is unknown if she met her fate by being poisoned by the Medusoid Mycelium. It is noted that the Incredibly Deadly Viper followed the boat with an apple, and as the Baudelaires did not know this, it is possible some islanders survived to report this to Lemony Snicket. Friday knew the snake to be friendly, and thus may have taken the apple from it; however, it is unknown if she would have been able to convince Sadie or the drugged islanders to eat it.
- Sadie's first name may refer to a character in Our Girl Friday, a 1953 British comedy film.
- The plot of the movie involves spoiled heiress Sadie and other characters winding up on a desert island, where relationship drama causes them to argue and squabble, possibly relating to the mutiny on The Island.
- The name of the film could also connect Sadie to fellow islander Friday Caliban.
- Her surname may refer to Samuel "Black Sam" Bellamy, an 18th-century pirate who was shipwrecked off Cape Cod.
- While she makes no physical appearance in the Netflix Adaptation of The End, she could still potentially be one of the unnamed islanders.