The letter was written while Thomas Butter was at Portsmouth and is addressed to his father W. James Butter. A voyage along the West Coast of Africa is described with stops at Ascension, Fernando Po, St Helena, Sierra Leone, Prince Island, Accra and Cameroon. During the voyage there have been extensive deaths from fever affecting several ships including HMS SYBILLE and EDEN, with most of the sick dying at Fernando Po. The affected ships resort to sailing south to St Helena for a colder climate to reduce the fever. The West African climate is described.
An anti-slavery patrol is mentioned wherein a slaving ship with 387 Africans were on board was captured followed a few days later by the capture of another slaving ship with 319 Africans on board after a 30-hour chase. However, the fever returns between these two successes and increases to the degree that the ship must once again sail to a colder climate. Several more deaths from the fever are recorded.
Butter gives the prize money he expects to receive for his voyage as at least one hundred pounds.

Administrative / biographical background
Following the Act for the Abolition of the Slave Trade in1807, the Royal Navy was used to supress the Atlantic slave trade. HMS SYBILLE was part of West Africa squadron and patrolled the coast looking for illegal slavers.