Possible Clues:

• Sea creature who lived across the Strait of Messina from Scylla
• Danger at sea daily repelled by detectives
• Sea monster of Greek myth able to make whirlpools
• Cautious, approaching infernal place occupied by black monster
• Whirlpool opposite Scylla
• Monster from hell approached by cautious bishop
• See 10-Down
• Cautious bids ordered — it was dangerous for old sailors
• Hard to avoid a wrecking with Biscay, a legendary shipping hazard
• Careful — heartless fellow is a monster!