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. 
For an unknown reason, 
I do not feel 100%.
Por un motivo desconocido, 
hoy no me siento al 100%.
Por lagún extraño motivo, hoy no me encuentro al 100%.
Por alguma razão, não me sinto 100%.