Rebecca and Carrie are invited by William's Great Aunt Ruthie to Bainbridge Island, Washington to investigate mysterious lights that have been seen underneath the Agate Pass Bridge late at night. Ruthie's elderly friends, along with Rebecca's parents, join in the investigation and participate in a stakeout on a cold, rainy night. The elements are against them, but Rebecca is determined to solve the puzzle. Glimpses of Island life from sixty years ago as well as today are chronicled in a fun, engaging story.
