The single sheet, dated from Twickenham, appeared to contain nothing more than a few lines of civility. The clerk at the Post Office held it before the fire: beneath the ordinary ink, a second text emerged, traced in lemon juice. It advised the French to effect a landing upon the English coast. The authorities thereupon set about discovering who had penned the missive, and under what name his other communications were passing.
Florence Hensey hailed from County Kildare, in Ireland. Bred in the Roman Catholic faith, he had learned his Latin under a priest, subsequently studying philosophy at Saint-Omer and medicine at Leyden. He had traversed Germany and Switzerland, visited Italy, and thence passed into Portugal, Spain, and France, acquiring the tongues of the countries through which he journeyed. In Paris, he practised physic for five years, though his affairs did not prosper. He removed to London, where his practice remained meager and confined to the common sort.
A former fellow student from Leyden had established himself in France and obtained an appointment under the Secretary of State in Paris. Hensey wrote to felicitate him, offering in passing to render such services as he might in London. Hostilities had just broken out between Great Britain and France. His friend suggested that he transmit intelligence touching British military preparations. Instructions presently followed, accompanied by the promise of remuneration. Hensey consented.
The intelligence demanded was precise: lists of the men-of-war, their condition, crews, ports, commanders, and destinations; the strength of the troops, the regiments at full complement, their quarters, and their garrisons. Hensey could glean no such particulars from his medical rounds. He sought first to ingratiate himself with clerks in the public offices, without success, and thereafter frequented the coffee-houses where members of Parliament were wont to gather. The doctor was held to be above suspicion. If he could not evade political disputation, he argued on the side of the government, displaying all the zeal of an adversary to the French.
The despatches quitted London by stages. Hensey addressed them to a correspondent in Cologne, who forwarded them to a contact in Bern, who in turn transmitted them to Paris; the post thus traveled by way of Switzerland. The replies returned along an analogous route, reaching London under an assumed name, addressed to a coffee-house in the Strand. To look upon the cover, one saw merely an exchange of courtesies between acquaintances. Their frequency, however, at length excited suspicion at the General Post Office.
The Secretary directed that certain letters be opened. In the sheet from Twickenham, the invisible writing appeared between the visible lines. The authorities did not content themselves with examining the paper: they resolved to discover the person who came to the coffee-house to receive it. A watch was placed upon the premises. Having collected a letter, Hensey returned to his lodgings in Arundel Street; the officer tracked him thither.
On the Sunday following, Hensey attended divine service, according to his custom, at the chapel of the Spanish Ambassador in Soho Square. As he returned, he was apprehended by two King’s messengers and conveyed to a place of security. After several examinations before the Secretary of State, he was committed to Newgate. He spoke little of his private concerns and admitted few visitors, saving his confessor.
The trial opened before the Court of King’s Bench at Westminster on June 12, 1758. The defense first challenged the venue of the indictment: the letters had been intercepted at the London Post Office, whereas the venue was laid in Middlesex. The Crown replied that one of the letters bore the date of Twickenham, within that county. Hensey’s counsel next submitted that a letter detained before reaching its destination had not been “published.” The Attorney General rejoined that the act of posting sufficed; the Court observed that a letter intended to convey aid to the enemy retained its treasonable quality notwithstanding its interception by the authorities. The defense further urged that the letters were addressed to Holland, with which power Great Britain was not at war.
The post-office officers deposed to the letters received and opened; other papers had been found in Hensey’s bureau. Apothecaries who had made up his prescriptions identified his handwriting. The defense objected likewise to two draft letters seized at his lodgings, contending that comparison of hands was insufficient to fix their authorship upon him. The Crown answered that witnesses had seen Hensey write, and that the papers were found in his custody. The Court admitted the exhibits, leaving their weight to the jury. At the close of the proceedings, Lord Mansfield proposed that the jury carry the letters with them into their retiring room, to which both sides consented. The sheets thus passed into the hands of the men entrusted with the physician’s life. In this prosecution, the provenance and course of the papers mattered as much as their text: the Crown had to prove that they were written by Hensey and intended for the enemy. His counsel called no witnesses for the defense, resting their case upon procedural exceptions and the legal construction of the correspondence.
While the jury deliberated, Hensey shook, turned pale, and wept, according to Borrow’s account. Upon their return, he had scarce the strength to hold up his hand. The verdict was guilty. Two days later, on June 14, sentence of death for high treason was pronounced upon him. He prayed for a respite to prepare for his end; the Court granted him a month. Borrow records that while in prison, Hensey was brought to pawn his sword and his linen to supply his immediate wants. After the years of study, the travels, and the correspondence that had filled his life, a few personal effects were thus bartered to sustain a convict already delivered over to the scaffold.
On the morning appointed for his execution, a reprieve arrived. It was subsequently replaced by a respite during His Majesty’s pleasure. The conviction remained, but the immediate peril of death was stayed. Hensey lay in Newgate while his brother, secretary and chaplain to the Spanish Ambassador at The Hague, made interest with the Spanish ambassador in London, who interceded with the English ministry. Borrow relates that a royal pardon was at length granted following the accession of George III, and that Hensey departed for France; a later biographical notice states that he was admitted to bail in 1759, after which he is lost to view. Neither account fixes with certainty the date of his final departure.