The case board begins with the famous mysteries of quantum mechanics: the measurement problem, the Born rule, the quantum-to-classical boundary, decoherence, objective collapse, Wigner's Friend, nonlocality without signaling, contextuality, the problem of time, quantum gravity, black-hole information, and the ontology of the wave function. These are the visible mountains of quantum foundations.

But Essie is not satisfied with visible mountains. She looks for the hidden infrastructure beneath them. A second catalogue examines the assumptions that often escape notice precisely because they make quantum calculation possible: the idealization of isolation, the origin of Hilbert space, the meaning of preparation, the status of the apparatus, the classical language problem, the fragility of phase, the reality of counterfactual outcomes, the scalability of quantum weirdness, the thermodynamics of information, the role of agency, the emergence of objectivity, and the silence of successful calculation.

The investigation then turns orthogonal. Why did Schrödinger's original steel chamber become the cultural "box"? Why is Wittgenstein not a canonical voice in the reception of a thought experiment so full of linguistic danger? Why does Gödel, the great logician of incompleteness and Einstein's Princeton companion, seem strangely absent from the quantum foundations debate over completeness? And how does Ettore Majorana's real disappearance become a human missing-person case at the edge of quantum history?

Essie, Quantum Cat Detective invites readers to see quantum mechanics not merely as strange, but as structured mystery. A good detective does not close a case too early. Essie does not either.

(Late development, the Gödel mystery and other Princetonian Puzzles are being investigated, and the detective work is paying off ... stay tuned for developments)