This article is for the book that Margaret writes secrets in. For information about the episode involving the diary, see here.Margaret's Diary is the name of a diary book which appeared in the episode, "Diary". In a diary, the owner is supposed to write secrets and stuff they only know in it. Margaret's diary, has a lock on it, which Mordecai and Rigby have to try to fix back up before Margaret returns home from a trip. They tried using super glue but they poured too much. They tried to melt the glue using the grill but the diary caught fire. Rigby then accidentally pours gasoline on it after mistaking it for water. Mordecai and Rigby then consulted Skips and Skips proposes to use a magic quill pen to recreate the diary. After Rigby peeks through the diary, the Guardian of Secrets was unleashed. The gang managed to defeat it and they successfully created an exact replica of Margaret's diary.
The book is red with a golden heart shaped lock on it.