It must be remembered that the mice already had a way to get inside your walls. In Florida, a state licensed pest control contractor must come to your home and inject a chemical inside the walls that the rodent eats. After ingestion, the rodent is driven outside and dies outside before returning. When that is accomplished, you can then repair the access where they got in, which will prevent them from returning in the future. If the smell remains after, the drywall will need to be removed, the interior chemically treated for cleaning/disinfecting purposes and new drywall or other surface (such as paneling/wood) installed.
Locate entrance and close it off. Place traps and poison where accessible to rodents.