Of all the shadowy and poorly understood periods of Macintosh’s life, the years he spent in what is now Germany are the most mysterious. I have written before on Macintosh’s residence in Eisenach, where he may have died (he certainly wrote his will there) at some point after 1810. The precise means and chronology of Macintosh’s relocation from Avignon (in the 1790s) to Eisenach (in the 1800s) have still to be sketched out, but there is some indication that he spent time in Stuttgart in the interim.
This fragment of information is contained in a letter sent from Berlin by Thomas Grenville (1755–1846) to his brother, William Grenville (1759–1834), on 4 March 1799. Tomas and William were sons of the late Whig prime minister George Grenville (1712–1770). Thomas, a member of parliament and privy councillor, had in 1799 been appointed ambassador to Berlin in order to broker an alliance against France as part of the War of the Second Coalition. In his letter to William, Thomas notes that
I was scarcely arrived here when I received a communication from Stutgard [sic], signed W. M’Intosh, and claiming to be known to you and to Mr. [George] Canning, which expresses the greatest apprehensions at the progress of the French principles in the duchy of Wirtemberg [sic] under the active directors of Citoyen Mengaud and Citoyen Trouvè, who are so good as to employ themselves with great zeal and success for that purpose 
It seems unlikely (to say the least) that Thomas’s correspondent was anyone other than William Macintosh. This fragment offers a useful further indication of Macintosh’s network of correspondents, but also opens up new lines of enquiry regarding Macintosh’s time in Stuttgart.
1. Historical Manuscripts Commission (1904) Report on the manuscripts of J. B. Fortescue, Esq., preserved at Dropmore. Vol. IV, p. 485.