Mo. Rev. Stat. § 443.330: Trustee failing to execute trust, parties interested may proceed, how.

If any trustee in any deed of trust to secure the payment of a debt or other liability shall die, or has died, shall become or has become mentally incapacitated, shall remove or has removed out of this state, shall neglect or refuse or has neglected or refused to act as such trustee, or shall or has become unable, by sickness or other disability, to perform or execute his trust, any person interested in the debt or other liability secured by such deed of trust, may present his or their affidavit, stating the facts of the case, specifically, to the circuit court of the county in which the property or estate conveyed by such deed of trust, or any part thereof, is situated.