Birthdays are always fun. Will many friends visit the little boy on his birthday? 'Knock, knock, knock!' Somebody is at the door. 'Who's there?' Why it's Cat! 'Happy Birthday!' Cat has appeared with a bouquet of flowers! 'Knock, knock, thump!' 'Who's there?' 'Come on in, Giraffe!' Giraffe greets the birthday child with a 'Happy Birthday!' and a nice picture book. Each unique knock on the door belongs to a dear friend. One by one, they arrive to join the birthday celebration.