The Last Whole Stone (Ground Truth, Book Four) by Gene Roth

Leila Moreno weighs a returned envelope of meteorite dust and finds it eleven point eight milligrams light.

At Caldera, a private foundation built entirely around knowing what happened to a thing between one measurement and the next, a gap that size is routine — logged, reconciled, forgotten by Monday. This one won't be.

Deep inside CMSF-01, one of three visibly different kinds of material returns a reading that looks, on the front page, like proof the stone predates the solar system itself. It doesn't. What the number actually says is narrower, harder to headline, and far more dangerous to the people now required to act on it.

Because years before anyone knew what the stone would say, the foundation's donor wrote a deed for exactly this moment: once a finding crosses a defined line, a ninety-day clock starts, and two stewards — one sworn to keep the stone whole, one sworn to prove the finding true everywhere it can be tested — must each choose what happens to what's left. Agree, and the stone can be cut apart to settle the question for good. Disagree, and it survives intact, unresolved, whole.

The Last Whole Stone is a novel about custody, about what a measurement is actually allowed to claim, and about the last ninety days in which one object can still be both things at once.