Matthew's party is given the letter in Kaocho, during a discussion with King Wo. Written by Wo's advisor Meisa, it is addressed to General Ku-Tsung, who is stationed in Ayuthay, and states that Matthew's party will assist with Kaocho's siege. The letter reads: "To Ku-Tsung, general of the Kaocho army: The courier of this letter, Matthew, has pledged his loyalty to our royal cause. This loyal servant and his companions have sworn to use their Psynergy to help you crush Ayuthay. -Wo, King of Kaocho"
Bringing the letter to Ayuthay will allow Matthew's party to bypass the guards blocking the entrance into Ayuthay. When brought to the palace, it triggers a cutscene with both the Kaocho generals. During the cutscene, the letter will be given to Ku-Tsung. Attempting to enter Ayuthay without the letter will cause Matthew's party to be denied entry by the guards, who are said to be waiting on orders.