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. 
But Gustave was actually 
sneaking out at night.
Pero en realidad Gustave estaba 
escabulléndose en la noche.
Pero en realidad, Gustave pensaba escabullirse en mitad de la noche.
Mas Gustava estava escapando a noite.