Crew is a type of Unit. Couple is a type of Unit. Couple is a synonym of Mate. 
you are likely to find Clue in/at/on Drawer. you are likely to find Marker in/at/on Drawer. 
Crew --IsA--> Unit <--IsA-- Couple <--Synonym--> Mate 
Clue --AtLocation--> Drawer <--AtLocation-- Marker 