Mo. Rev. Stat. § 429.140: Duty of contractor when others file lien.

In all cases where a lien shall be filed under the provisions of sections 429.010 to 429.340 by any person other than a contractor, it shall be the duty of the contractor to defend any action brought thereupon, at his own expense; and, during the pendency of such action, the owner may withhold from the contractor the amount of money for which such lien shall be filed; and in case of judgment against the owner or his property upon the lien, he shall be entitled to deduct from any amount due by him to the contractor the amount of such judgment and costs, and, if he shall have settled with the contractor in full, shall be entitled to recover back from the contractor any amount so paid by the owner for which the contractor was originally the party liable.