Captain Reynell quitted Grenada early in 1798, in consequence of being appointed assistant adjutant-general at St. Domingo, where he remained until that island was evacuated by the British in September, when he returned to England. In the beginning of 1799 he revisited St. Domingo, as one of the suite of Brigadier-General the Honorable Thomas Maitland, then employed in framing a commercial treaty with the negro chief Toussaint L’Ouverture, who had risen to the supreme authority at St. Domingo. When it was concluded, Captain Reynell returned to England in July of the same year. On the 8th of August 1799 Captain Reynell was transferred to a company in the fortieth regiment, with the first battalion of which he embarked for the Helder in that month, and joined the army, which was at first commanded by Lieut.-General Sir Ralph Abercromby, and afterwards by the Duke of York. Captain Reynell was present in the action of the 10th of September; also in the battle of the 19th of September, when he was the only captain of the first battalion of the fortieth regiment that was not killed or wounded; he was also present in the subsequent battles of the 2d and 6th of October. Captain Reynell, upon the British army being withdrawn from Holland, re-embarked with the first battalion of the fortieth regiment, and arrived in England in November 1799. In April 1800 Captain Reynell embarked with his regiment for the Mediterranean, and went in the first instance to Minorca, afterwards to Leghorn; returned to Minorca, and proceeded with a large force under Lieut.-General Sir Ralph Abercromby for the attack of Cadiz. Signals for disembarking were made; but although the boats had actually put off from the ships, a recall was ordered, in consequence of the plague raging at Cadiz. After this he proceeded up the Mediterranean again, and in November landed at Malta.