One Big Unicorn is the puppet book that Gru writes at the end of the movie. It is the story of his life. He does this in part because he doesn't like the girls' favorite bedtime story "Three Sleepy Kittens", but mostly he wants to show Margo, Edith and Agnes how much they have helped him, even though he pretends that they have nothing to to with the making of One Big Unicorn. ("Any relation to persons living or dead is completly coincidential.") Margo, Edith and Agnes love it when Gru reads them the story, and Agnes even exclaims "This is going to be the best book ever!!"