The Case of the Lost Treasure — Dean Wesley Smith

Hired by heirs to find two million in treasure hidden in a completely empty house, Pilgrim Hugh finds himself stuck.
The house sparkles and no stick of furniture remains.
Original house plans show clearly that no room hid behind any walls. And millions of dollars in cash takes up a bunch of room. But where?
A puzzle mystery that stumps for a short time even the great Pilgrim Hugh.