To Stop a Steele

Plot:

Ms. Holt is hired (as long as Steele is not involved) by jeweler, Albert Harrod, to locate an stolen flawless 60 carat diamond that had been "hidden" among much less expensive items. Mr. Steele is hired (as long the agency is not involved) by jewel thief, Morrie Singer. He was commissioned to burgle the Harrod gem vault, but found it empty. Who has the hot rocks and are the two different cases involving the same jeweler connected?