The letter presents a plan for a citadel designed by Détalonde Morival, whose rapid progress in mathematics and engineering is described as extraordinary. The author criticises complex mathematical pursuits as unnecessary, emphasising the practical value of a good engineer over abstract calculations. He advocates for Morival, a noble and capable soldie, to be employed in the service of the sovereign, highlighting his skills, dedication, and loyalty. Nearing the end of his life, the author seeks comfort in the sovereign’s continued support for Morival, asserting that such support would be a just response to the injustices Morival has faced.

Additionally, according to T. D. N. Besterman, the letter is dated 2 January 1775.

The author presents to the King a drawing of the Battle of Rossbach by D’Étalonde, emphasising the deep admiration and devotion of an officer eager to serve in such campaigns. He expresses gratitude for the King’s support, noting its effect on strengthening the officer’s loyalty, and observes that the latter is more intent on serving under the King than seeking favour in France.

He further commends the King’s ability to combine attention to major affairs with personal consideration, and contrasts this with the recently less impressive French coronation, underscoring instead the King’s multifaceted and exemplary leadership.

The writer expresses deep personal loyalty to the monarch and refers to reports that Cosinski and other conspirators swore a religious oath to the Virgin Mary before attempting their crime. He observes, with irony, that many notorious assassins have also been deeply religious.

He suggests that the monarch’s presence, virtues, and humanity may have awakened natural feelings of compassion in the would-be assassin, counteracting the influence of religious fanaticism. The writer further argues that this event will ultimately reinforce the monarch’s authority and render rebellion shameful. He requests a brief reply to be sent to Geneva and closes with renewed expressions of respect and devotion.