The backrooms of the British Museum are bristling with sleuths. Irving Finkel, an expert in the world's oldest writing, is called to Scotland Yard to help the police with their enquiries. In the museum's laboratory, Rebecca Stacey is hunting for a whiff of opium in a small pot three and a half thousand years old. And Colin McEwan is trying to crack a code, the silent language of the Nasca, the ancient and mysterious South American tribe, famous for etching huge symbols in the Peruvian desert. Colin thinks the key to these symbols lies in some dusty boxes on the museum's shelves.