1 detective

2 to do detective work

1 to explore

2 to search out

3 to scout

4 to visit

5 to stretch forward

1 to explore

2 to probe

1 to explore

2 to survey

3 to prospect (for oil etc)

4 prospecting

1 secret agent

2 detective

3 covert investigator

1 to poke one's head in and pry (idiom); to spy

2 nosy

1 to feel in one's pocket and take sth (idiom); as easy as pie

2 in the bag

1 to stick one's head out and look around (idiom)

1 to pluck a pearl from the black dragon (idiom, from Zhuangzi); fig. to pick out the salient points (from a tangled situation)

2 to see through to the nub