In February 1808, "Agamemnon" sailed with Rear-Admiral Sir Sidney Smith's flagship to Brazil, where they joined another squadron. At Rio de Janeiro it was discovered that "Agamemnon" was again quite worn out, with seams in her planking opening and some of her framing bolts broken. In October, "Agamemnon" and anchored in Maldonado Bay, in the mouth of the River Plate. They had been escorting the merchant vessel "Maria", which had carried the surgeon Dr. James Paroissien to Montevideo where he was tasked with exposing a plot against King John VI of Portugal, who was in exile in Brazil. Whilst there, "Monarch" ran aground, requiring "Agamemnon"s assistance to get her off. After learning that Paroissien had been imprisoned, the two ships put to sea, but were forced to return to Maldonado Bay when they encountered bad weather. After the ships returned to Rio in January 1809, the ship was fully surveyed by the carpenter, who drew up an extensive list of her defects.