The Adventure of the Beryl Coronet recap

Banker Alexander Holder accepts the beryl coronet as security for a loan from an exalted client and takes it home for safekeeping. During the night he finds his indebted son Arthur holding the bent coronet, with three stones missing, and has him arrested. Holmes studies the house, the snow outside, and the strength needed to break the gold setting. He discovers that Holder's niece Mary had given the coronet to Sir George Burnwell. Arthur witnessed the exchange, fought Burnwell, and recovered part of the treasure, but kept silent to protect Mary. Holmes obtains the missing beryls from Burnwell. Mary flees with him, while Holder learns that the son he condemned was acting out of loyalty.

Alexander Holder, a prominent banker, lends a large sum to a highly placed client who leaves the beryl coronet as security. Holder fears the treasure will not be safe at his office and carries it to his home. There he tells his son Arthur, his niece Mary, and the household staff that a valuable object is in his room. Arthur, already in debt, asks his father for money and is refused. That night Holder wakes to a noise and finds Arthur gripping the coronet. Its setting is bent and three beryls are gone. Arthur will not explain himself, so Holder has him arrested and asks Holmes to recover the stones before the loss becomes a public scandal. Holmes tests Holder's account against the physical evidence. The gold cannot have been broken silently by one person indoors, and marks in the snow show that a struggle occurred outside. Holmes concludes that Mary secretly handed the coronet to Sir George Burnwell. Arthur saw them, pursued Burnwell, and recovered the larger broken section after a fight, then remained silent to shield Mary. Holmes confronts Burnwell and buys back the missing gems. Mary has already run away with Burnwell. Holder can repair the royal treasure and clear Arthur, but must face the fact that he distrusted the loyal member of his family and trusted the one who betrayed him.

Holmes proves that Arthur was trying to recover the coronet rather than steal it. Arthur had seen Mary pass the treasure to Sir George Burnwell and followed Burnwell outside, where the two men struggled. The coronet broke during the fight, and Arthur returned with the portion he had recovered. He accepted arrest rather than expose Mary, whom he loved. Holmes tracks Burnwell down and compels him to surrender the three missing beryls in exchange for payment. Mary has fled with Burnwell, leaving a note behind, and Holder recognizes that his suspicion wronged his son. The gems can be restored to the coronet, but the damage to the family cannot be so neatly repaired.