A pair of schoolgirl friends, their bedridden companion, and a reserved new classmate uncover clues in an old house that lead from attic discoveries to a lost sapphire signet. The narrative follows their investigation as curiosities, hidden trunks, and a key prompt local historical research by an ally named Alexander and members of an antiquarian club. Surprises and belated revelations connect personal histories, secret documents, and missing links until the signet's significance is revealed and loose ends are tied. The book mixes domestic detail, youthful camaraderie, and puzzle-solving with gentle suspense.