Mr Neat and Mr Tidy (who, strangely, are humans not Mr Men) clean up Mr Messy's house against his wishes. Then they clean up him. At the end, he seems happy about the change (though he looks much better to me before his makeover).
My two year old loves his book. I'd like it better if Mr Neat and Mr Tidy were Mr Men and/or if the cleaning of Mr Messy wasn't against his will.