"There's an acoustical freak in Gouffre Martel... they happen in underground caves... a freak of echoes, passages and whispering galleries. Old-timers call it the Whisper Line. I never believed them. No one ever did, but it's true. We're talking to each other over the Whisper Line. No one can hear us but us. We can talk, Foyle. We can plan. Maybe we can escape."