Possible Clues:

• ___ into (examine)
• Dig, as for information
• Search deeply (into)
• I can't get into 'To be or not to be' options -- dig?
• Leaders of life-saving volunteers go into river and probe deeply
• Dig — investigate
• Model very content during search
• Led this back at first to dig with it
• Digit in spades?
• Research key provided by centre in Slovenia