Espionage is a trade which notoriously attracts practitioners who are not of a common mould, and this was as true of the eighteenth century as it is of the twentieth. The engineer Le Turc was not a man who fitted into norms or had much patience with the regular, the commonplace or the humdrum. He had little money sense; he was no businessman; he read the details of contracts he entered into through a visual filter which permitted him only to absorb the clauses which were favourable to him. He confessed an ‘inconstancy’ which prevented him following up most favourable career opportunities with a sensible steadiness. If there was a man so constituted as to arouse antipathies in bureaucrats, it was he. Over the last three decades of the eighteenth century, and under both the ancien régime and the Revolution, he antagonized important ministers, influential officials, enlightened intellectuals, celebrated scientists, many of whom could have been, and some of whom tried to be, his patrons and protectors. Certainly towards the end of his life his hold on reality had become tenuous and erratic, and he could probably be defined as paranoid.