Mo. Rev. Stat. § 484.130: Compensation of attorney governed by agreement — lien upon client's cause of action.

The compensation of an attorney or counselor for his services is governed by agreement, express or implied, which is not restrained by law. From the commencement of an action or the service of an answer containing a counterclaim, the attorney who appears for a party has a lien upon his client's cause of action or counterclaim, which attaches to a verdict, report, decision or judgment in his client's favor, and the proceeds thereof in whosesoever hands they may come; and cannot be affected by any settlement between the parties before or after judgment.