Hazel Peabody is a ten year old girl living in New York City. One very rainy day, Hazel is stuck in her apartment with her cat Casper wondering if it will ever stop raining. She decides to look at the assignment her teacher, Mrs. Lovelock has given to her class. She discovers that her class has been asked to write a paper on the loch Ness monster. Hazel thinks this a crazy thing to ask her class to write about since "everyone knows that there's no such thing as the loch Ness monster." She decides instead to take a nap.
Hazel is suddenly awakened by noises coming from her closet. It sounds like water dripping. She thinks that there must be a leak in the roof and that all her clothes will be ruined. She then hears what sounds like a whistle. Like that heard on an old naval ship. Hazel looks at her cat Casper and says, "now that's really weird." Hazel finally decides to open her closet door and see what's going on. She turns the knob and suddenly the doors blows off it's hinges with a great gust of wind. She and Casper hide under her bed.
The next things she sees is her next door neighbor, Mr. Peachtree, dressed as a pirate. He has a patch over one eye and a wooden peg leg where his real leg used to be. Hazel asks him what he is doing in her closet, and why he is dressed the way he is. Mr. Peachtree tells her it's all part of the adventure to find the loch Ness monster. He tells her that a ship is waiting for them to board and be on their way. Hazel is a bit hesitant, but then she hears her friends Trudy and Poo calling her to join them from inside her closet. She decides that since her friends are on board, it must be okay. With that Hazel and Casper follow Mr. Peachtree across the threshold of her closet and onto the great ship Petunia.
And so the adventure begins...