The Rescuers Wiki

In an abandoned river boat in Devil's Bayou, Penny, a young orphan, drops a message in a bottle containing a plea for help into the river. The bottle is carried out to sea and washes up in New York City, where it is recovered by the Rescue Aid Society, an international mouse organization inside the United Nations. The Hungarian representative, Miss Bianca, volunteers to accept the case and chooses Bernard, a stammering janitor who has triskaidekaphobia, as her co-agent. The two visit Morningside Orphanage, where Penny lived, and meet an old cat named Rufus. He tells them about a woman named Madame Medusa who once tried to lure Penny into her car and may have succeeded in abuducting Penny this time.
The mice travel to Medusa's pawn shop, where they discover that she and her partner, Mr. Snoops, are on a quest to find the world's largest diamond, the Devil's Eye. They also discover that Mr. Snoops is in the Devil's Bayou with Penny, whom they have indeed kidnapped. With the help of an albatross named Orville, and a dragonfly named Evinrude, the mice follow Medusa to the bayou. There, they learn that Penny was captured to enter a hole that leads down into the pirates' cave where the Devil's Eye is located.