Related Clues:

• Use a peephole, say
• One who prowls
• 007, e.g
• Mata Hari was one
• Le Carre character, or Saskatchewan hill
• Plant, maybe
• One seeking intelligence
• Gain intelligence
• Tiptoe, perhaps
• Skulking sort
• Binoculars user
• Watch from the bushes
• Behave furtively
• Sort of snake in the grass
• Sly person