William R. Sauer (defendant) sought medical treatment at Missouri Baptist Hospital on June 6, 1984, where he claimed to have insurance coverage through Blue Cross Health Services, Inc. (Blue Cross) (plaintiff). Sauer did not have current coverage, and the hospital mistakenly associated him with William J. Sauer in their computer system, who did have insurance coverage through Blue Cross. The hospital changed the address of William J. Sauer to match the address given by William R. Sauer, which was the address of William R. Sauer’s father’s business. Subsequently, Blue Cross mistakenly mailed six checks intended for William J. Sauer to this new address. These checks totaled more than $22,000 and were cashed or deposited by William R. Sauer, his father, or his father’s business (defendants). Blue Cross eventually discovered the mistake and filed a suit in equity seeking a constructive trust upon the funds of the defendants based on unjust enrichment. Blue Cross originally sued William R. Sauer and his father’s business. Approximately three years after the original suit was filed, Blue Cross added the father as a defendant. The defendants moved for a transfer to a law division from the equity division and sought a jury trial. The trial court denied those motions and held a non-jury trial. The trial court entered judgment against the defendants. However, the trial court then granted a new trial, ruling that the defendants had been entitled to a jury trial. Blue Cross appealed to the Missouri Court of Appeals.