Maria Gibson, née Pinto, is a woman whose death is investigated by Sherlock Holmes. Maria was the daughter of a Brazilian government official from Manaos. She met Neil Gibson, an American gold prospector, while he was in Brazil to survey the Amazon, and the two began a passionate romance that culminated in their marriage. Gibson returned to America with his wife, where he built himself a reputation as one of the greatest gold-mining magnates in the world and served as senator for a western state. However, Mr Gibson's affections for his wife soon cooled, and he grew increasingly distant from her although his wife remained enamored.

After a number of years together the couple had two children and moved to England, where Mr Gibson had purchased a large estate in Hampshire called Thor Place. The family lived there together mostly uneventfully for five years, during which time Mr Gibson hired Grace Dunbar as a governess for the children. Mr Gibson began pursuing Miss Dunbar romantically, much to Maria's fury.

Mrs Gibson was eventually found dead on a bridge on the estate after meeting with Grace Dunbar, and the police arrested the governess for murder. The police believed Grace had killed Maria to remove her as an obstacle to her marriage with Mr Gibson. However, Holmes discovered that Maria actually committed suicide and framed Grace for her death after becoming jealous when she discovered that Grace and her husband were in a relationship.

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