What is the burden of a fiduciary on a plaintiff to prove that entrusted funds were not improperly used?

While Plaintiffs argue that under the principles enunciated in Otto v. Niles (In re Niles) , 106 F.3d 1465 (9th Cir. 1997), once the use of entrusted money is shown, then the burden shifts to the fiduciary to show that the use was not improper. However, this claim is premised on there being a partnership, which the court cannot determine on this summary judgment motion based on the evidence presented.