Sir Thomas lived in the 16th century.
When Matilda received the letter she said that she did not want to hide her true purpose for much longer. Then she explained that Trent should tell Sir Thomas that the deed would be done by daybreak. She further mentioned that Jane Grey would die that night.
This Matilda tried to kill Jane Grey, but was stopped by Rani Chandra. Matilda later said that she wanted Jane to become a martyr. Her death would have inspired thousands to rise up against Mary. (TV: Lost in Time)