Gustave has taken it upon himself to observe Marion and Sanglain following the death of the Princess and DT.   But KT thinks Gustave is in the city of Marquesas for other reasons. 
How do you know what I was thinking?
¿Cómo sabes en qué estoy pensando?
¿Cómo sabes en qué estoy pensando?
Como você sabe o que
eu estava pensando?