The Yellow House Mystery by Gertrude Chandler Warner

Four siblings discover clues in a long-abandoned yellow house that connect to their grandfather’s vanished friend, who disappeared years ago after borrowing money. Determined to learn the truth, they follow a trail of letters, maps, and hidden caches across lakes and islands, uncovering a story of loyalty and mistaken suspicion. Their search leads to a remote hideout, where they clear the man’s name and help bring about a heartfelt reunion.

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