After the opening credits we are introduced to the Rescue Aid Society, an International mouse organization, a meeting of which has been convened because the society has received an urgent request for help. Although the message, printed in pencil on lined paper, was in a bottle, it has been damaged by water. Studying it carefully, Miss Bianca can read little except 'Hurry!" and the name Penny. She is moved with compassion and immediately volunteers for the rescue mission, even though she still knows almost nothing about the little girl who wrote the message.