Mo. Rev. Stat. § 408.050
No person shall directly or indirectly take, for the use or loan of money or other commodity, above the rates of interest specified in sections 408.020 to 408.040, for the forbearance or use of one hundred dollars, or the value thereof, for one year, and so after those rates for a greater or less sum, or for a longer or shorter time, or according to those rates or proportions, for the loan of any money or other commodity. Any person who shall violate the foregoing prohibition of this section shall be subject to be sued, for any and all sums of money paid in excess of the principal and legal rate of interest of any loan, by the borrower, or in case of borrower's death, by the administrator or executor of his estate, and shall be adjudged to pay the costs of suit, including a reasonable attorney's fee to be determined by the court.
§ 408.050, RSMo
RSMo 1939 § 3229