Mo. Rev. Stat. § 535.090: Complaint, contents — proof of trial.

It shall be sufficient for such person purchasing lands or tenements to file a complaint, pursuant to section 535.070, verified by affidavit, stating by whom the premises were leased or rented, and the terms of such lease or renting, and how such person claims title to the lands or tenements; and upon the trial of the cause, if the plaintiff shows that the party in possession, or those under whom the party in possession claims, rented or leased from a party claiming title to the premises by deed, and that the plaintiff has acquired the title of the original lessor or landlord, by a deed or deeds, regularly acknowledged, the plaintiff shall be entitled to recover possession and unpaid rent accruing after the transfer and while the tenant was in possession.