- Alexander Holder – One partner in a private bank that's known for loaning money to wealthy families. Holmes's client.
- Arthur Holder – Alexander's gambler son, suspected of stealing a piece of the Beryl Coronet.
- Mary Holder – Alexander's niece and adopted daughter.
- Sir George Burnwell – One of Arthur's worthless friends: a bad influence! Frequently visits the Holder family.
- Lucy Parr – The new maid, whom Mary suspects of theft.
- Francis Prosper – The new maid's wooden-legged beloved, suspected of conspiring with Lucy.
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