Mo. Rev. Stat. § 510.130
1. A plaintiff shall be allowed to dismiss his action without prejudice at any time before the same is finally submitted to the jury, or to the court sitting as a jury, or to the court, and not afterward. A plaintiff who has once so dismissed his action and thereafter files another action upon the same claim shall not be allowed to dismiss the same without prejudice after the jury has been impaneled, or after evidence has been introduced in a nonjury case, except
(L. 1943 p. 353 § 99)
(1972) Plaintiff does not have an absolute right to take a voluntary dismissal but to deny such dismissal, defendant must show some injury to himself more than the mere fact that plaintiff could bring another action. Stubblefield v. Seals (Mo.), 485 S.W.2d 126.